Kevin M. Bell

Effect of Tunnel-Graft Length on the Biomechanics of Anterior Cruciate Ligament–Reconstructed Knees Intra-articular Study in a Goat Model

Background In anterior cruciate ligament (ACL) reconstruction using hamstring grafts, the graft can be looped, resulting in an increased graft diameter but reducing graft length within the tunnels. Hypothesis After 6 and 12 weeks, structural properties and knee kinematics after soft tissue ACL reconstruction with 15 mm within the femoral tunnel will be significantly inferior when compared with the properties of ACL reconstruction with 25 mm in the tunnel. Study Design Controlled laboratory study. Methods In an intra-articular goat model, 36 ACL reconstructions using an Achilles tendon split graft were performed with 15-mm (18 knees) and 25-mm (18 knees) graft length in the femoral tunnel. Animals were sacrificed 6 weeks and 12 weeks after surgery and knee kinematics was tested. In situ forces as well as the structural properties were determined and compared with those in an intact control group. Histologic analyses were performed in 2 animals in each group 6 and 12 weeks postoperatively. Statistical analysis was performed using a 2-factor analysis of variance test. Results Anterior cruciate ligament reconstructions with 15 mm resulted in significantly less anterior tibial translation after 6 weeks (P < .05) but not after 12 weeks. Kinematics after 12 weeks and in situ forces of the replacement grafts at both time points showed no statistically significant differences. Stiffness, ultimate failure load, and ultimate stress revealed no statistically significant differences between the 15-mm group and the 25-mm group. Conclusion The results suggest that there is no negative correlation between short graft length (15 mm) in the femoral tunnel and the resulting knee kinematics and structural properties. Clinical Relevance Various clinical scenarios exist in which the length of available graft that could be pulled into the bone tunnel (femoral or tibial) could be in question. To address this concern, this study showed that reducing the tendon graft length in the femoral bone tunnel from 25 mm to 15 mm did not have adverse affects in a goat model.

Development of a simple device for measurement of rotational knee laxity

The goal of this study was to develop a new device for the measurement of rotational knee laxity and to measure intra-observer and inter-observer reliability in a cadaveric study. An array of established tools was utilized to design the device with a basis that consists of an Aircast Foam Walker™ boot. A load cell was attached to the boot with a handle bar for application of moments about the knee. An electromagnetic tracking system was used to record the motion of the tibia with respect to the femur. The total arc of motion ranged from 23° at full extension to 46° at 90° of knee flexion. The intra-tester ICCs ranged from 0.94 to 0.99. The ICC for inter-tester reliability ranged from 0.95 to 0.99. In summary, the new device for measurement of rotational knee laxity is simple, reliable, and can be used in a non-invasive fashion in the office or surgical suite document clinical outcome in terms of rotational knee laxity.

Rotational knee laxity: Reliability of a simple measurement device in vivo

BackgroundDouble bundle ACL reconstruction has been demonstrated to decrease rotational knee laxity. However, there is no simple, commercially-available device to measure knee rotation. The investigators developed a simple, non-invasive device to measure knee rotation. In conjunction with a rigid boot to rotate the tibia and a force/moment sensor to allow precise determination of torque about the knee, a magnetic tracking system measures the axial rotation of the tibia with respect to the femur. This device has been shown to have acceptable levels of test re-test reliability to measure knee rotation in cadaveric knees.MethodsThe objective of this study was to determine reliability of the device in measuring knee rotation of human subjects. Specifically, the intra-tester reliability within a single testing session, test-retest reliability between two testing sessions, and inter-tester reliability were assessed for 11 male subjects with normal knees.ResultsThe 95% confidence interval for rotation was less than 5° for intra-tester, test-retest, and inter-tester reliability, and the standard error of measurement for the differences between left and right knees was found to be less than 3°.ConclusionIt was found that the knee rotation measurements obtained with this device have acceptable limits of reliability for clinical use and interpretation.

Assessing range of motion to evaluate the adverse effects of ill-fitting cervical orthoses.

BACKGROUND CONTEXT Although previous studies have primarily focused on testing the effectiveness of cervical orthoses under properly fit conditions, this study focuses on analyzing the effects of an ill-fitted cervical orthosis (Miami J). This may have significance to health-care providers in understanding the effects of an improperly fitted neck brace. PURPOSE The aims of this study were threefold: first, to apply virtual reality (VR) feedback control to repeatedly measure orthoses effectiveness in the primary motions; second, to use this control methodology to test the orthoses ability to restrict flexion/extension (FE) as a function of axial rotation (AR); third, to test the effects of an ill-fitting Miami J on cervical motion. STUDY DESIGN/SETTING This study combines six degrees of freedom electromagnetic trackers and VR feedback to analyze the effectiveness of common cervical orthoses under less than optimal conditions. PATIENT SAMPLE Twelve healthy male subjects aged 21 to 35 (mean 29.44 years, SD 6.598) years with no previous spinal cord injuries or current neck pain participated in the study. OUTCOME MEASURES Cervical range of motion (CRoM) measurements were used to determine the amount of motion restriction for each of the fitted (too small, correct size, and too big) Miami J orthoses. METHODS One Nest of Birds (NOB) electromagnetic sensor (Ascension Technology) was placed on the head and another on the upper back to measure motion of the head relative to the torso. The VR goggles (i-O Display Systems) were worn so that real-time feedback was available to the subject for motion control. The subject executed the primary motions of FE, AR, and lateral bending (LB) in separate sets of five trials each. Next, in combined motion, the subject axially rotated to a set point and then FE to his maximums. This entire set of motions was repeated for each (soft collar, Miami J, Miami J with chest extension, Sternal Occipital Mandibular Immobilizer (AliMed, Inc.), (SOMI and Halo) as well as the Miami J (one size too small and one size too big); the fitting of each brace was done by a board certified orthotist. A repeated measures analysis of variance was used to determine differences between the tested states (*p=.05). RESULTS For the validation test, the primary motions recorded for subjects wearing each cervical brace, which demonstrated that the various orthoses all restricted CRoM. The soft collar restricted less motion than the other devices, whereas the Halo restricted the most motion throughout. For the ill-fitting cervical collar comparison, motion in the correct size collar was normalized to 1.0, and the correct size allowed less motion than either the too big or too small braces. In FE, the too big brace tended to allow more motion than the too small, but only the too big brace in extension was significantly different from the correct size. In AR, the too small brace seemed to allow more motion than the too big. Both the too big and too small braces were significantly different than the correct size in both left and right AR. In LB, the too big brace and too small brace were very similar in the amount of motion they were able to restrict. Both braces were significantly different than the correct size in right LB, whereas only the too small brace was significantly different from the correct size in left LB. In the combined motion data, both the too big and too small braces allowed more motion than the correct size. The too small brace seemed to allow more FE at all degrees of AR except for extreme right AR. CONCLUSIONS To our knowledge, the effects of improperly fitted cervical orthoses on CRoM are still unknown. Using the NOB electromagnetic tracking system combined with VR feedback, we were able to consider the motion restriction of ill-fitting Miami J orthoses for both primary and combined motions. For both motion types, increased motion was possible when the subject was improperly fitted with the Miami J. If not considered, these excessive motions could potentially have detrimental effects on patient satisfaction, clinical outcomes, or even lead to increased secondary injury.

Injection of human umbilical tissue–derived cells into the nucleus pulposus alters the course of intervertebral disc degeneration in vivo

BACKGROUND CONTEXT Patients often present to spine clinic with evidence of intervertebral disc degeneration (IDD). If conservative management fails, a safe and effective injection directly into the disc might be preferable to the risks and morbidity of surgery. PURPOSE To determine whether injecting human umbilical tissue-derived cells (hUTC) into the nucleus pulposus (NP) might improve the course of IDD. DESIGN Prospective, randomized, blinded placebo-controlled in vivo study. PATIENT SAMPLE Skeletally mature New Zealand white rabbits. OUTCOME MEASURES Degree of IDD based on magnetic resonance imaging (MRI), biomechanics, and histology. METHODS Thirty skeletally mature New Zealand white rabbits were used in a previously validated rabbit annulotomy model for IDD. Discs L2-L3, L3-L4, and L4-L5 were surgically exposed and punctured to induce degeneration and then 3 weeks later the same discs were injected with hUTC with or without a hydrogel carrier. Serial MRIs obtained at 0, 3, 6, and 12 weeks were analyzed for evidence of degeneration qualitatively and quantitatively via NP area and MRI Index. The rabbits were sacrificed at 12 weeks and discs L4-L5 were analyzed histologically. The L3-L4 discs were fixed to a robotic arm and subjected to uniaxial compression, and viscoelastic displacement curves were generated. RESULTS Qualitatively, the MRIs demonstrated no evidence of degeneration in the control group over the course of 12 weeks. The punctured group yielded MRIs with the evidence of disc height loss and darkening, suggestive of degeneration. The three treatment groups (cells alone, carrier alone, or cells+carrier) generated MRIs with less qualitative evidence of degeneration than the punctured group. MRI Index and area for the cell and the cell+carrier groups were significantly distinct from the punctured group at 12 weeks. The carrier group generated MRI data that fell between control and punctured values but failed to reach a statistically significant difference from the punctured values. There were no statistically significant MRI differences among the three treatment groups. The treated groups also demonstrated viscoelastic properties that were distinct from the control and punctured values, with the cell curve more similar to the punctured curve and the carrier curve and carrier+cells curve more similar to the control curve (although no creep differences achieved statistical significance). There was some histological evidence of improved cellularity and disc architecture in the treated discs compared with the punctured discs. CONCLUSIONS Treatment of degenerating rabbit intervertebral discs with hUTC in a hydrogel carrier solution might help restore the MRI, histological, and biomechanical properties toward those of nondegenerated controls. Treatment with cells in saline or a hydrogel carrier devoid of cells also might help restore some imaging, architectural, and physical properties to the degenerating disc. These data support the potential use of therapeutic cells in the treatment of disc degeneration.

Alterations in gene expression in response to compression of nucleus pulposus cells

BACKGROUND CONTEXT It is clear that mechanical forces are involved in initiating disc degeneration but also have the potential to exert beneficial effects. However, the signaling pathways initiated by mechanical stress and thresholds for these responses have not been elucidated. We have developed a metabolically active compression system with the advantages of having the ability to test cells in vitro as well as within their native matrix and control exposure to environmental factors. We hypothesized that nucleus pulposus cells would respond to compressive stress with different thresholds for alterations in catabolic and anabolic gene expression. PURPOSE The purpose of the study was to establish the utility of a novel compression chamber and examine the effects of various magnitudes and durations of compression on nucleus pulposus inflammatory, catabolic, and anabolic gene expression. STUDY DESIGN In vitro controlled examination of intervertebral disc cell responses to compression. METHODS A chamber capable of imparting 0 to 20 MPa of hydrostatic compression onto nucleus pulposus cells was fabricated. Healthy rabbit nucleus pulposus cells were cultured in alginate beads and exposed to static compression at 0.7, 2, and 4 MPa for 4 or 24 hours. Gene expression analysis (real-time polymerase chain reaction) was performed to compare markers of inflammation (inducible nitric oxide synthase, cyclooxygenase-2), matrix catabolism (matrix metalloproteinase-3), and anticatabolic/anabolic metabolism (tissue inhibitor of metalloproteinase-1, aggrecan) in control and compressed cells. RESULTS Compression resulted in magnitude- and duration-dependent changes in gene expression. Increasing magnitudes showed more anticatabolic gene expression changes, whereas increasing duration resulted in increases in procatabolic gene expression. CONCLUSION These data demonstrate favorable effects of compression in relation to genes involved in matrix homeostasis and procatabolic gene expression in response to sustained loading levels, consistent with traumatic effects. These data provide an improved understanding of how compression affects cell signaling, which has the potential to be exploited to initiate repair and prevent matrix breakdown.

The Anterolateral Capsule of the Knee Behaves Like a Sheet of Fibrous Tissue

Background: The function of the anterolateral capsule of the knee has not been clearly defined. However, the contribution of this region of the capsule to knee stability in comparison with other anterolateral structures can be determined by the relative force that each structure carries during loading of the knee. Purpose/Hypothesis: The purpose of this study was to determine the forces in the anterolateral structures of the intact and anterior cruciate ligament (ACL)–deficient knee in response to an anterior tibial load and internal tibial torque. It was hypothesized that the anterolateral capsule would not function like a traditional ligament (ie, transmitting forces only along its longitudinal axis). Study Design: Controlled laboratory study. Methods: Loads (134-N anterior tibial load and 7-N·m internal tibial torque) were applied continuously during flexion to 7 fresh-frozen cadaveric knees in the intact and ACL-deficient state using a robotic testing system. The lateral collateral ligament (LCL) and the anterolateral capsule were separated from the surrounding tissue and from each other. This was done by performing 3 vertical incisions: lateral to the LCL, medial to the LCL, and lateral to the Gerdy tubercle. Attachments of the LCL and anterolateral capsule were detached from the underlying tissue (ie, meniscus), leaving the insertions and origins intact. The force distribution in the anterolateral capsule, ACL, and LCL was then determined at 30°, 60°, and 90° of knee flexion using the principle of superposition. Results: In the intact knee, the force in the ACL in response to an anterior tibial load was greater than that in the other structures (P < .001). However, in response to an internal tibial torque, no significant differences were found between the ACL, LCL, and forces transmitted between each region of the anterolateral capsule after capsule separation. The anterolateral capsule experienced smaller forces (~50% less) compared with the other structures (P = .048). For the ACL-deficient knee in response to an anterior tibial load, the force transmitted between each region of the anterolateral capsule was 434% greater than was the force in the anterolateral capsule (P < .001) and 54% greater than the force in the LCL (P = .036) at 30° of flexion. In response to an internal tibial torque at 30°, 60°, or 90° of knee flexion, no significant differences were found between the force transmitted between each region of the anterolateral capsule and the LCL. The force in the anterolateral capsule was significantly smaller than that in the other structures at all knee flexion angles for both loading conditions (P = .004 for anterior tibial load and P = .04 for internal tibial torque). Conclusion: The anterolateral capsule carries negligible forces in the longitudinal direction, and the forces transmitted between regions of the capsule were similar to the forces carried by the other structures at the knee, suggesting that it does not function as a traditional ligament. Thus, the anterolateral capsule should be considered a sheet of tissue. Clinical Relevance: Surgical repair techniques for the anterolateral capsule should restore the ability of the tissue to transmit forces between adjacent regions of the capsule rather than along its longitudinal axis.

Novel technique for evaluation of knee function continuously through the range of flexion

Previous research has utilized robots to examine joint kinematics and in situ forces in response to loads applied at discrete flexion angles (static method). Recently, studies have applied loads continuously throughout flexion (continuous flexion method). However, the joint kinematics resulting from each of these methods have not been directly compared. Therefore, the objective of this study was to utilize a robotic testing system to compare kinematics and in situ forces of porcine knees in response to 89 N of anterior tibial load and 4 Nm of internal tibial torque between the static method (loads applied at 30°, 45°, 60°, and 75° of flexion) and the continuous flexion method (measured continuously from 30-75° of flexion) for both the anterior cruciate ligament (ACL) intact and ACL deficient (ACLD) knees. When anterior tibial load was applied the average differences in anterior tibial translation between the two methods for the intact state was 0.5±0.0 mm and for the ACLD state was 0.3±0.2 mm. The difference in the in situ forces in the ACL was 1.6±0.9 N. When internal tibial torque was applied the average differences in the resultant internal tibial rotation for the intact state was 0.9±0.4° and for the ACLD state was 1.0±0.5°. The difference in the in situ forces in the ACL was 3.3±2.0 N. Both methods are equally efficient in detecting significant differences (p<0.05) between intact and ACL deficient knee states. The continuous flexion method was also shown to be more efficient than the static method and provides continuous data on knee function throughout the range of motion.

Influence of varying compressive loading methods on physiologic motion patterns in the cervical spine.

The human cervical spine supports substantial compressive load in-vivo arising from muscle forces and the weight of the head. However, the traditional in-vitro testing methods rarely include compressive loads, especially in investigations of multi-segment cervical spine constructs. Various methods of modeling physiologic loading have been reported in the literature including axial forces produced with inclined loading plates, eccentric axial force application, follower load, as well as attempts to individually apply/model muscle forces in-vitro. The importance of proper compressive loading to recreate the segmental motion patterns exhibited in-vivo has been highlighted in previous studies. However, appropriate methods of representing the weight of head and muscle loading are currently unknown. Therefore, a systematic comparison of standard pure moment with no compressive loading versus published and novel compressive loading techniques (follower load - FL, axial load - AL, and combined load - CL) was performed. The present study is unique in that a direct comparison to continuous cervical kinematics over the entire extension to flexion motion path was possible through an ongoing intra-institutional collaboration. The pure moment testing protocol without compression or with the application of follower load was not able to replicate the typical in-vivo segmental motion patterns throughout the entire motion path. Axial load or a combination of axial and follower load was necessary to mimic the in-vivo segmental contributions at the extremes of the extension-flexion motion path. It is hypothesized that dynamically altering the compressive loading throughout the motion path is necessary to mimic the segmental contribution patterns exhibited in-vivo.

Influence of number of operated levels and postoperative time on active range of motion following anterior cervical decompression and fusion procedures.

Study Design. A cohort study analyzing the cervical range of motion of subjects with anterior cervical decompression and fusion operation (ACDF). Objective. The purpose of this study was to compare the cervical range of motion of subjects who underwent an ACDF operation to age-matched healthy nonoperative subjects. Subjects were divided according to the number of operated levels, postoperative time point, and level of disability. Summary of Background Data. ACDF is an operative treatment aimed at expansion of the spinal canal and relief of cord compression. In addition to alleviating pain, 2 common tools are used to measure postoperative success; cervical range of motion kinematic analysis and subjective evaluation questionnaires (Neck Disability Index [NDI]). Methods. This study involved 25 preoperative and 110 postoperative ACDF subjects as well as 18 control volunteers with no prior history of neck complaints. ACDF subjects were divided according to the number of operated levels; 1-, 2-, 3-, and 4-levels as well as time of their clinical visit; preoperative, early, and late postoperative. Before kinematic testing, the subjects were asked to complete the NDI survey. A virtual reality assisted electromagnetic tracking was used to measure an active voluntary motion of the head relative to the torso. The subjects’ maximum range of motion was calculated and compared as they executed 3 to 5 consecutive cycles of the primary motions, flexion/extension, axial rotation, and lateral bending. An analysis of variance statistical test (P < 0.01) was used to determine significant differences between study groups. Results. Subjects range of motion decreased relative to control as the number of operated levels increased. Moreover, 1- and 2-level subjects increased their range motion relative to preoperative. Finally, there was a decrease in range of motion as the subjects level of disability increased as measured by an NDI score but all subjects reported a lower score relative to preoperative time point. Conclusion. The active range of motion of subjects who underwent an ACDF surgery increased postoperative and was dependent on the number of operated levels. In addition, there was an improvement in the disability level after the surgery as measured by the NDI score.