Is the native ACL insertion site "completely restored" using an individualized approach to single-bundle ACL-R?

PURPOSE: The goal of individualized anatomic anterior cruciate ligament reconstruction (ACL-R) is to reproduce each patient's native insertion site as closely as possible. The amount of the native insertion site that is recreated by the tunnel aperture area is currently unknown, as are the implications of the degree of coverage. As such, the goals of this study are to determine whether individualized anatomic ACL-R techniques can maximally fill the native insertion site and to attempt to establish a crude measure to evaluate the percentage of reconstructed area as a first step towards elucidating the implications of complete footprint restoration. METHODS: This is a prospective pilot study of 45 patients who underwent primary single-bundle anatomic ACL-R from May 2011 to April 2012. Length and width of the native insertion site were measured intraoperatively. Using published guidelines, reconstruction technique and graft choice were determined to maximize the percentage of reconstructed area. Native femoral and tibial insertion site area and femoral tunnel aperture area were calculated using the formula for area of an ellipse. On the tibial side, tunnel aperture area was calculated with respect to drill diameter and drill guide angle. Percentage of reconstructed area was calculated by dividing total tunnel aperture area by the native insertion site area. RESULTS: The mean areas for the native femoral and tibial insertion sites were 83 ± 20 and 125 ± 20 mm(2), respectively. The mean tunnel aperture area for the femoral side was 65 ± 17, and 86 ± 17 mm(2) for the tibial tunnel aperture area. On average, percentage of reconstructed area was 79 ± 13 % for the femoral side, and 70 ± 12 % for the tibial side. CONCLUSION: Anatomic ACL-R does not restore the native insertion site in its entirety. Percentage of reconstructed area serves as a rudimentary tool for evaluating the degree of native insertion site coverage using current individualized anatomic techniques and provides a starting point from which to evaluate the clinical significance of complete footprint restoration. LEVEL OF EVIDENCE: IV.

Patient-specific knee joint finite element model validation with high-accuracy kinematics from biplane dynamic Roentgen stereogrammetric analysis.

Little is known about in vivo menisci loads and displacements in the knee during strenuous activities. A new method that combines high-speed kinematics measured with biplane dynamic Roentgen stereogrammetric analysis (DRSA) and a subject-specific finite element (FE) model for studying in vivo meniscal behavior is presented here. Further model calibration in a very controlled uniaxial low and high-rate compression loading condition is presented by comparing the model behavior against the measured high-accuracy menisci DRSA kinematics and direct tibio-femoral pressure measurement from a K-scan sensor. It is apparent that certain model aspects such as removing of the pressure sensor from the model can result in relatively large errors (14%) in contact parameters that are not reflected in the change of the measured meniscal kinematics. Changing mesh size to 1mm by 1mm elements increased the magnitude of all but one of the contact variables by up to 45%. This local validation using accurate localized patient-specific geometry and meniscal kinematics was needed to enhance model fidelity at the level of contact between menisci and cartilage.

Sensitivity of the tibio-femoral response to finite element modeling parameters.

A generic finite element (FE) model of the lower limb was used to study the knee response in-vivo during a one-legged hop. The approach uses an explicit FE code and a combination of estimated muscle forces and measured three-dimensional tibio-femoral kinematics and ground reaction force as input to the FE model. The sensitivity of the simulated tibio-femoral response to variations of key geometric and material parameters was investigated by performing a total of 38 different simulations. The amplitudes of both kinematic and kinetic responses were affected by the change of these parameters. For the current approach, the results suggest that while cartilage mechanical and geometric properties are very important for the estimation of tibio-femoral cartilage pressure, they have limited effects on the overall kinematic response. The study may help to better define the relative importance of modeling parameters for the development of subject-specific models.

In vivo serial joint space measurements during dynamic loading in a canine model of osteoarthritis.

OBJECTIVE: To devise a reliable, sensitive method to measure joint space in vivo during dynamic loading. Additionally, to determine if dynamic joint space changes were related to the severity of long-term cartilage damage. DESIGN: Subjects were 23 adult foxhounds (18 experimental, 5 control). Experimental subjects had surgically transected cranial cruciate ligaments (CCL). Dynamic joint space was serially measured in vivo over 2 years using a unique high speed stereo radiographic system in combination with subject-specific computed tomography reconstructions. RESULTS: Dynamic joint space was measured in vivo with a within-day precision of 0.09 mm. Half of the experimental subjects developed minor articular cartilage damage and the other half developed severe articular cartilage damage in the medial knee compartment. Joint space during treadmill running increased significantly in the minor damage group in both the medial (+0.61 mm, P = 0.036) and lateral (+0.84 mm, P = 0.002) compartments of the knee. Dynamic joint space in the severe damage group did not increase significantly on either the medial (+0.27 mm, P = 0.408) or lateral (+0.44 mm, P = 0.199) side. The majority of the change in joint space occurred the first year after CCL transection. Medial meniscus damage was related to severity of medial articular cartilage damage (tau = 0.447, P = 0.003). The minor damage group developed 73% of all osteophytes noted at dissection. CONCLUSIONS: This technique is a precise tool for measuring joint space serially in vivo under dynamic loading conditions. The data suggest decreased severity in long-term articular cartilage damage is related to: osteophyte formation, less severe medial meniscus damage and increased joint space the first 12 months after injury.

A new method to investigate in vivo knee behavior using a finite element model of the lower limb.

Several finite element models have been developed for estimating the mechanical response of joint internal structures, where direct or indirect in vivo measurement is difficult or impossible. The quality of the predictions made by those models is largely dependent on the quality of the experimental data (e.g. load/displacement) used to drive them. Also numerical problems have been described in the literature when using implicit finite element techniques to simulate problems that involve contacts and large displacements. In this study, a unique strategy was developed combining high accuracy in vivo three-dimensional kinematics and a lower limb finite element model based on explicit finite element techniques. The method presents an analytical technique applied to a dynamic loading condition (impact during hopping on one leg). The validation of the lower limb model focused on the response of the whole model and the knee joint in particular to the imposed 3D femoral in vivo kinematics and ground reaction forces. The approach outlined in this study introduces a generic tool for the study of in vivo knee joint behavior.

In vivo measurement of 3-D skeletal kinematics from sequences of biplane radiographs: application to knee kinematics.

Current noninvasive or minimally invasive methods for evaluating in vivo knee kinematics are inadequate for accurate determination of dynamic joint function due to limited accuracy and/or insufficient sampling rates. A three-dimensional (3-D) model-based method is presented to estimate skeletal motion of the knee from high-speed sequences of biplane radiographs. The method implicitly assumes that geometrical features cannot be detected reliably and an exact segmentation of bone edges is not always feasible. An existing biplane radiograph system was simulated as two separate single-plane radiograph systems. Position and orientation of the underlying bone was determined for each single-plane view by generating projections through a 3-D volumetric model (from computed tomography), and producing an image (digitally reconstructed radiograph) similar (based on texture information and rough edges of bone) to the two-dimensional radiographs. The absolute 3-D pose was determined using known imaging geometry of the biplane radiograph system and a 3-D line intersection method. Results were compared to data of known accuracy, obtained from a previously established bone-implanted marker method. Difference of controlled in vitro tests was on the order of 0.5 mm for translation and 1.4 degrees for rotation. A biplane radiograph sequence of a canine hindlimb during treadmill walking was used for in vivo testing, with differences on the order of 0.8 mm for translation and 2.5 degrees for rotation.

Investigation of Head Injury Mechanisms Using Neutral Density Technology and High-Speed Biplanar X-ray.

The principal focus of this study was the measurement of relative brain motion with respect to the skull using a high-speed, biplanar x-ray system and neutral density targets (NDTs). A suspension fixture was used for testing of inverted, perfused, human cadaver heads. Each specimen was subjected to multiple tests, either struck at rest using a 152-mm-diameter padded impactor face, or stopped against an angled surface from steady-state motion. The impacts were to the frontal and occipital regions. An array of multiple NDTs was implanted in a double-column scheme of 5 and 6 targets, with 10 mm between targets in each column and 80 mm between columns. These columns were implanted in the temporoparietal and occipitoparietal regions. The impacts produced peak resultant accelerations of 10 to 150 g, and peak angular accelerations between 1000 and 8000 rad/s(2). For all but one test, the peak angular speeds ranged from 17 to 22 rad/s. The relative 3D displacements between the skull and the NDTs were analyzed. The localized motions of the brain generally followed loop or figure eight patterns, with peak displacements on the order of +/- 5 mm. These results can be used to further finite-element modeling efforts.

Qualitative analysis of neck kinematics during low-speed rear-end impact.

OBJECTIVE: To analyze neck kinematics and loading patterns during rear-end impacts. DESIGN: The motion of each cervical vertebra was captured using a 250 frame/s X-ray system during a whole body rear-end impact. These data were analyzed in order to understand different phases of neck loading during rear-end impact. BACKGROUND: The mechanism of whiplash injury remains largely unknown. An understanding of the underlying kinematics of whiplash is crucial to the identification of possible injury mechanisms before countermeasures can be designed. METHODS: Metallic markers were inserted into the vertebral bodies and spinous processes of each of the seven cervical vertebrae. Relative displacement-time traces between each pair of adjacent cervical vertebrae were calculated from X-ray data. Qualitative analyses of the kinematics of the neck at different phase of impact were performed. RESULTS: The neck experiences compression, tension, shear, flexion and extension at different cervical levels and/or during different stages of the whiplash event. CONCLUSIONS: Neck kinematics during whiplash is rather complicated and greatly influenced by the rotation of the thoracic spine, which occurs as a result of the straightening of the kyphotic thoracic curvature. RELEVANCE: Understanding the complicated kinematics of a rear-end impact may help clinicians and researchers shed some light on potential mechanisms of whiplash neck injury.

The Case Western Reserve University hybrid gait orthosis.

Six individuals with paraplegia and injury levels from C-1 through T-12 participated in a study to evaluate the functional capabilities of a hybrid gait orthotic system. Subjects learned to use a custom-built reciprocal gait orthosis without stimulation and with electrical stimulation activating between 4 and 16 muscles. Outcomes were scored with standard physical therapy measures including the Tinetti test, a timed get up and go, Borg rating of perceived exertion, and the Functional Index Measure (FIM). Subjects have successfully accomplished sit to stand, stand to sit, and walking maneuvers measured for time, speed, and distance. Metabolic consumption was measured for walking in the light work region of 5.1 to 6.5 metabolic equivalents (METs) 1 MET = 3.5 ml of O2/kg/min with hybrid gait orthosis. Perceived exertion as measured with the Borg scale indicated that use of the bracing system with functional electrical stimulation was "easier" than without stimulation. Subjects using a hybrid system were able to walk up to 350 m at average speeds of 0.25 m/s. Walking speeds for 30- and 50-meter distances reached 0.45 m/s. Additionally, walking distances with stimulation were 2 times greater than those of non-stimulated reciprocal gait. FIM scores indicated that system users would become slightly more independent in mobility. Results were used to determine the most useful brace modifications for the next generation of Case Western Reserve University hybrid gait orthoses to allow an expanded function that will include stair climbing and side stepping.

Kinematics of human cadaver cervical spine during low speed rear-end impacts.

The purposes of this study were to measure the relative linear and angular displacements of each pair of adjacent cervical vertebrae and to compute changes in distance between two adjacent facet joint landmarks during low posterior-anterior (+Gx) acceleration without significant hyperextension of the head. A total of twentysix low speed rear-end impacts were conducted using six postmortem human specimens. Each cadaver was instrumented with two to three neck targets embedded in each cervical vertebra and nine accelerometers on the head. Sequential x-ray images were collected and analyzed. Two seatback orientations were studied. In the global coordinate system, the head, the cervical vertebrae, and the first or second thoracic vertebra (T1 or T2) were in extension during rear-end impacts. The head showed less extension in comparison with the cervical spine. Relative motion for each cervical motion segment went from flexion at the upper cervical levels to extension at the lower cervical levels, with a transition region at the mid-cervical levels. This rotational pattern formed an "S" shape in the cervical spine during the initial phase of low-speed rear impacts. A pair of facet joint landmarks on each cervical motion segment was used to measure the distance across the joint space. Uni-axial facet capsular strains were calculated by dividing changes in this distance over the original distance in seven tests using three specimens. In 20-degree seatback tests, the average strain was 32+/-11% for the C2/C3 facet joint (17%-43% range), and 59+/-26% for the C3/C4 facet joint (41%-97% range). The C4/C5 and C5/C6 facet joints exhibited peak tensile or compressive strains in different specimens. In 0-degree seatback tests, the average strain was 28+/-11% for the C2/C3 facet joint (21%-41% range), 30+/-9% for the C3/C4 facet joint (21%-39% range), 22+/-4% for the C4/C5 facet joint (19%-25% range), and 60+/-13% for the C5/C6 facet joint (51%-69% range). In 20-degree seatback tests, there was less initial cervical lordosis, more upward ramping of the thoracic spine, and more relative rotation of each cervical motion segment in comparison with the 0-degree seatback tests. Relative to T1, the head went from flexion to extension for 20-degree seatback tests while stayed in extension for 0-degree seatback tests.

Scaphoid fracture displacement with forearm rotation in a short-arm thumb spica cast.

Three-dimensional motion between the fragments of an experimental scaphoid waist fracture was measured during dynamic forearm pronation and supination in a short-arm thumb spica cast with and without applied tendon loads. Metal markers placed in each fragment were tracked using high-speed biplane radiographic image sequences and stereophotogrammetric analysis. Peak displacements (from the intact state) exceeded 1 mm in all specimens, with the largest movements occurring in the radial direction during pronation (mean: 2.1 mm unloaded, 2.5 mm loaded). Total range of displacement motion between fragments exceeded 3 mm (mean ulnar/radial direction: 3.4 mm unloaded, 4.1 mm loaded). Dorsal/palmar and proximal/distal displacements were minimal except at the extremes of forearm pronation/supination. Rotations between fragments were small (within +/- 6 degrees) and varied considerably across specimens. No significant differences were found between loaded and unloaded trials. Thus, in the absence of long-arm thumb spica casting to limit forearm rotation, significant motion between the fragments of a scaphoid waist fracture is likely.

Modeling and simulation of paraplegic ambulation in a reciprocating gait orthosis.

We developed a three dimensional, four segment, eight-degree-of-freedom model for the analysis of paraplegic ambulation in a reciprocating gait orthosis (RGO). Model development was guided by experimental analysis of a spinal cord injured individual walking in an RGO with the additional assistance of arm crutches. Body forces and torques required to produce a dynamic simulation of the RGO gait swing phase were found by solving an optimal control problem to track the recorded kinematics and ground reaction forces. We found that high upper body forces are required, not only during swing but probably also during double support to compensate for the deceleration of the body during swing, which is due to the pelvic thrust necessary to swing the leg forward. Other stimulations showed that upper body forces and body deceleration during swing can be reduced substantially by producing a ballistic swing. Functional neuromuscular stimulation of the hip musculature during double support would then be required, however, to establish the initial conditions needed in a ballistic swing.

Swing phase control with knee friction in juvenile amputees.

Above-knee amputees have a slower than normal walking velocity. In conventional prostheses the solution has been to apply knee friction to attempt to match the cadence of the prosthetic limb to the sound limb. Using kinematic data, we investigated the effect of variable knee friction on the swing phase of gait in juvenile amputees. The subjects were instructed to walk at a comfortable pace and were tested repeatedly with varying amounts of knee friction. We found that the excursion of the prosthetic shank as measured by knee range of motion was altered by changing the amount of knee friction. The period of the prosthetic shank remained constant when measured as a physical pendulum and when measured dynamically during gait. Therefore, knee friction is an effective means of providing the amputee with a more symmetrical appearing gait by matching the heel rise of the prosthetic limb to the sound limb. It is not an effective means, however, of matching the cadence of the prosthetic limb to the sound limb.

Pre- and postoperative gait analysis in patients with spastic diplegia: a preliminary report.

The benefits of using computerized gait analysis to plan and evaluate operations were assessed by studying the data from 20 children with spastic diplegia and examining the changes in estimated external work of walking, stride length, walking velocity, and joint rotations pre- and postoperatively. Of the 20 patients, 13 improved, 6 were unchanged, and 1 was worse. None of the patients walked in a crouch postoperatively. By clinical evaluation, 19 of the 20 patients were better. Thus objective gait analysis imposed much more stringent criteria for improvement. Computerized gait analysis has enabled us to be more objective in the evaluation and documentation of outcome.