Daniel R. Sturnick

Geometric Risk Factors Associated With Noncontact Anterior Cruciate Ligament Graft Rupture

Background: Anterior cruciate ligament (ACL) graft rupture occurs at a high rate, especially in young athletes. The geometries of the tibial plateau and femoral intercondylar notch are risk factors for first-time ACL injury; however, little is known about the relationship between these geometries and risk of ACL graft rupture. Hypothesis: The geometric risk factors for noncontact graft rupture are similar to those previously identified for first-time noncontact ACL injury, and sex-specific differences exist. Study Design: Case-control study; Level of evidence, 3. Methods: Eleven subjects who suffered a noncontact ACL graft rupture and 44 subjects who underwent ACL reconstruction but did not experience graft rupture were included in the study. Using magnetic resonance imaging, the geometries of the tibial plateau subchondral bone, articular cartilage, meniscus, tibial spines, and femoral notch were measured. Risk factors associated with ACL graft rupture were identified using Cox regression. Results: The following were associated with increased risk of ACL graft injury in males: increased posterior-inferior–directed slope of the articular cartilage in the lateral tibial plateau measured at 2 locations (hazard ratio [HR] = 1.50, P = .029; HR = 1.39, P = .006), increased volume (HR = 1.45, P = .01) and anteroposterior length (HR = 1.34, P = .0023) of the medial tibial spine, and increased length (HR = 1.18, P = .0005) and mediolateral width (HR = 2.19, P = .0004) of the lateral tibial spine. In females, the following were associated with increased risk of injury: decreased volume (HR = 0.45, P = .02) and height (HR = 0.46, P = .02) of the medial tibial spine, decreased slope of the lateral tibial subchondral bone (HR = 0.72, P = .01), decreased height of the posterior horn of the medial meniscus (HR = 0.09, P = .001), and decreased intercondylar notch width at the anterior attachment of the ACL (HR = 0.72, P = .02). Conclusion: The geometric risk factors for ACL graft rupture are different for males and females. For females, a decreased femoral intercondylar notch width and a decreased height of the posterior medial meniscus were risk factors for ACL graft rupture that have also been found to be risk factors for first-time injury. There were no risk factors in common between ACL graft injury and first-time ACL injury for males.

Cadaveric gait simulation reproduces foot and ankle kinematics from population-specific inputs.

Cadaveric gait simulation allows researchers to directly investigate biomechanical consequences of surgeries using invasive measurement techniques. However, it is unclear if foot and ankle kinematics that are population‐specific are reproduced using these devices. Therefore, we assessed foot and ankle kinematics produced in a cadaveric gait simulator during the stance phase of gait in a set of five cadaveric feet. Tibial motions and ground reaction forces previously collected in vivo in a group of healthy adults were applied as inputs parameters. In vitro foot and ankle kinematics were acquired and directly compared to population‐specific in vivo kinematics of the same healthy adults from which input parameters were acquired. Analyses were completed using cross correlation to determine the similarities in kinematic profiles and joint ranges of motion were calculated to determine absolute differences in kinematics. Ankle, subtalar, and talonavicular in vitro joint kinematics were positively correlated to in vivo joint kinematics (rxy = 0.57–0.87). Further, in vivo and in vitro foot and ankle kinematics demonstrated similar amounts of within‐group variability (rxy = 0.50–0.85 and rxy = 0.72–0.76, respectively). Our findings demonstrate that cadaveric gait simulation techniques reproduce population‐specific foot and ankle kinematics, providing a valuable research tool for testing surgical treatments of foot and ankle maladies.

Relationship between geometry of the extensor mechanism of the knee and risk of anterior cruciate ligament injury.

The complex inter‐segmental forces that are developed across an extended knee by body weight and contraction of the quadriceps muscle group transmits an anteriorly directed force on the tibia that strain the anterior cruciate ligament (ACL). We hypothesized that a relationship exists between geometry of the knees extensor mechanism and the risk of sustaining a non‐contact ACL injury. Geometry of the extensor mechanism was characterized using MRI scans of the knees of 88 subjects that suffered their first non‐contact ACL injury and 88 matched control subjects with normal knees that were on the same team. The orientation of the patellar tendon axis was measured relative to the femoral flexion–extension axis to determine the extensor moment arm (EMA), and relative to tibial long axis to measure coronal patellar tendon angle (CPTA) and sagittal patellar tendon angle (SPTA). Associations between these parameters and ACL injury risk were tested with and without adjustment for flexion and internal rotation position of the tibia relative to the femur during MRI data acquisition. After adjustment for internal rotation position of the tibia relative to the femur there were no associations between EMA, CPTA, and SPTA and risk of suffering an ACL injury. However, increased internal rotation position of the tibia relative to the femur was significantly associated with increased risk of ACL injury in female athletes both in univariate analysis (Odds Ratio = 1.16 per degree of internal rotation of the tibia, p = 0.002), as well as after adjustment for EMA, CPTA, and SPTA.:

Influence of Tibial Component Position on Altered Kinematics Following Total Ankle Arthroplasty During Simulated Gait

Introduction/Purpose: Correct positioning of total ankle arthroplasty (TAA) implants has been associated with superior clinical outcomes. Furthermore, biomechanical studies have demonstrated that poor alignment of the components may lead to early component wear, compromising the longevity of the prosthesis. Malpositioning of TAA implants affects ligament engagement patterns and joint contact mechanics, possibly leading to altered joint kinematics. However, the correlation between implant position and ankle joint motion is still unclear. The objective of this study was to assess the effect of tibial component position on ankle kinematics following TAA during simulated gait.

Use of CT Scan-derived Patient-specific Instrumentation in Total Ankle Arthroplasty

Abstract: Total ankle arthroplasty has evolved significantly in the last 2 decades. Improvements in surgical technique and instrumentation, as well as advances in implant design, have contributed significantly to the increased adoption of ankle replacement for the treatment of ankle arthritis. Achieving proper alignment and correct positioning of the components is critical for the function and survivorship of the prosthesis. Patient-specific instrumentation generated by preoperative computed tomography is a tool which may allow for more reliable and reproducible component positioning. This article will provide a brief review of the technique and our early results of utilizing patient-specific instrumentation in total ankle arthroplasty. Level of Evidence: Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The Function Axis of Rotation of the Ankle Joint during Simulated Gait

Category: Ankle, Ankle Arthritis, Hindfoot Introduction/Purpose: Implant component positioning is considered as an important factor in function and longevity in total ankle arthroplasty (TAA). However, accurate and repeatable positioning remains a limitation with current techniques and instrumentation. In addition, further investigation is needed to objectively define the optimum component positioning. Cadaveric gait simulation is a valuable tool for investigating foot and ankle joint mechanics during functional tasks such as the stance phase of gait. The objective of this study was to investigate the functional axis of rotation of the native ankle joint during simulated gait. Methods: The stance phase of healthy gait was simulated with six mid-tibia cadaveric specimens using a previously validated device and methodology. A robotic platform reproduced tibial-ground kinematics by moving a force plate relative to the stationary specimen while physiologic loads were applied to the extrinsic tendons to actuate the foot. (Figure 1A). Ankle kinematics were measured from reflective markers attached to the tibia and talus via surgical pins. The helical axes of rotation of the talus with respect to the tibia was calculated during three portions of stance: initial plantarflexion during earlier-stance after heal strike, dorsiflexion during mid-stance, and final plantarflexion during late-stance. The position and orientation of these kinematic-defined axes of rotation were compared to the transmalleolar axis and reduced to its anteroposterior position and transverse plane angle (Figure 1B). Results: Analyses revealed that ankle joint functional axis of rotation varied from the anatomic reference throughout stance. The kinematic center of rotation was located 16.4 ± 5.8 mm, 16.5 ± 6.6 mm, and 15.6 ± 6.5 mm anterior to the transmalleolar axis during early-, mid- and late-portions of stance, respectively. Conclusion: This study revealed that the position of the flexion-extension axis varies greatly between specimens during simulated gait. While previous reports have suggested that the transmalleolar axis is an acceptable approximation for the ankle joint center, these findings suggest that further research in warranted to better describe the complex tibiotalar kinematics. This work may provide future insight to guide implant design and advance techniques, to better place articular constraints of a total ankle in the native center of rotation of the joint.

Ankle and Hindfoot Kinematics After Total Ankle Arthroplasty in Cadaveric Gait Simulation

Category: Ankle Arthritis. Introduction/Purpose: Total ankle arthroplasty (TAA) is an effective treatment option for end-stage ankle arthritis. However, with reports on long-term survivorship of current implant designs still anticipated in the literature, current research has focused on assessing prosthetic function and predicting potential failure mechanisms. Cadaveric gait simulation is a valuable tool for investigating the effects of surgical techniques on foot and ankle biomechanics. The objective of this study was to assess the effect of TAA on ankle and hindfoot kinematics using cadaveric gait simulation. We hypothesized that joint motion would be altered by the change in the articular constraint associated with joint replacement. Methods: Three mid-tibia cadaveric specimens were secured to a static mounting fixture about a six-degree of freedom robotic platform. A force plate was moved relative to the stationary specimen through an inverse tibial kinematic path calculated from in vivo data. Target tendon force profiles were applied to the nine extrinsic ankle tendons by linear actuators instrumented with load cells. (Figure 1A). Ankle and hindfoot kinematics were measured from reflective markers attached to bones via surgical pins. TAA was performed using the Salto Talaris prosthesis (Bloomington, MN). After replacing the ankle joint, foot and ankle kinematics were directly measured using the same kinematic inputs and muscle force as the intact condition. To assess the effect of TAA on joint kinematics, pre- and post-TAA motions were directly compared throughout the stance phase, and differences were assessed using two-tailed, paired Student’s t-tests with an alpha value set at p = 0.05. Results: Analyses revealed that ankle joint transverse plane motion was affected by TAA, with significantly greater talar internal rotation during the middle portion of stance after joint replacement (Figure 1B). In contrast, no differences were present in ankle joint sagittal and coronal plane motion between the intact and TAA condition. Dorsiflexion was greater in the subtalar joint after TAA during early stance. Similarly, there was greater dorsiflexion in the talonavicular joint during mid-stance in the TAA condition compared to the intact condition. There were no differences observed in the coronal or axial plane in either the subtalar or talonavicular joint after TAA. Conclusion: This study revealed that the talus underwent greater internal rotation during the weight acceptance portion of gait after TAA. The ankle joint however behaved similarly with respect to sagittal and coronal plane motion throughout stance after TAA. Compensatory motion however was noted in the subtalar and talonavicular joints, with greater dorsiflexion present in both joints during stance after TAA. This abstract represents an early subset of an ongoing study; smaller yet clinically important differences may still be present, and may be detected as more specimens are completed.

Effect of Subtalar Arthrodesis on Gait Kinematics in the Setting of Total Ankle Arthroplasty: A Study of Cadaveric Gait Simulation

Category: Ankle Arthritis Introduction/Purpose: Patients undergoing total ankle arthroplasty (TAA) often have symptomatic adjacent joint arthritis and deformity. Adjunctive procedures are frequently indicated in this setting in an attempt to ensure a stable and plantigrade ankle and hindfoot postoperatively. Although subtalar arthrodesis can effectively address a degenerative hindfoot, it may also place abnormal stress on the TAA, leading to premature failure. The objective of this study was to determine the effect of subtalar arthrodesis on TAA and adjacent joint kinematics using cadaveric gait simulation. We hypothesized that differences in ankle and talonavicular joint kinematics would be observed between TAA specimens with and without subtalar arthrodesis. Methods: Three mid-tibia cadaveric specimens (all female, average age at death: 48) with neutral foot alignment and no history of lower extremity trauma or surgery were tested in a robotic gait simulator. Each tibia was secured to a static mounting fixture about a six-degree of freedom robotic platform (Figure 1A). During simulations, a force plate was moved relative to the stationary specimen through an inverse tibial kinematic path based on standardized in vivo data. Salto Talaris total ankle prostheses were implanted (Tornier, Inc., Bloomington, MN) by a foot and ankle fellowship trained orthopaedic surgeon. Gait simulation was then performed. Each specimen then underwent in situ subtalar arthrodesis via fluoroscopically guided screw placement and subsequent gait analysis. The kinematics of TAA and TAA with subtalar arthrodesis during simulated walking were then compared using two-tailed, paired Student’s t-tests with an alpha value set at p = 0.05. Results: Analyses revealed that kinematics differed between specimens with TAA and those with TAA and subtalar arthrodesis (Figure 1B). During mid-stance, less ankle plantarflexion was observed in specimens with TAA and subtalar arthrodesis, as compared to those with isolated TAA. This difference was statistically significant (p < 0.05). With regard to axial motion in the ankle, significantly less external rotation was observed in early and mid-stance in specimens with TAA + subtalar arthrodesis (p < 0.05). Talonavicular kinematics also differed between cohorts (Figure 1B). In early and late stance, significantly decreased inversion was observed in specimens with subtalar arthrodesis (p < 0.05). And in early stance, talonavicular joint adduction was significantly diminished in the TAA + subtalar arthrodesis specimens, as compared to those with isolated TAA (p < 0.05). Conclusion: Via cadaveric gait simulation, our study describes the kinematic effects of subtalar arthrodesis on TAA. When TAA is performed in the setting of subtalar arthrodesis, both ankle sagittal and axial plane motion are altered, as are coronal and axial plane motion in the talonavicular joint. Because current clinical literature remains inconclusive on this relationship, additional work must be performed to better delineate the biomechanical and clinical sequelae of TAA performed with subtalar arthrodesis.

Adjacent Joint Kinematics after Ankle Arthrodesis in Cadaveric Gait Simulation

Category: Ankle Arthritis Introduction/Purpose: Ankle arthrodesis is an effective treatment for decreasing pain in patients with end-stage ankle arthritis. However, all patients with an ankle arthrodesis will eventually develop adjacent joint arthritis. The etiology of adjacent joint arthritis after ankle arthrodesis is not fully understood due to the difficulty of investigating these joints in vivo. Cadaveric simulation provides a unique capability of studying intrinsic foot and ankle joint mechanics. The objective of this study was to establish the effect of ankle arthrodesis on adjacent joint kinematics using cadaveric gait simulation. We hypothesized that adjacent joint motion of the hindfoot would increase after ankle arthrodesis. Methods: Four mid-tibia cadaveric specimens were potted and secured to a static mounting fixture about a six-degree of freedom robotic platform.(Figure 1A) The nine extrinsic ankle tendons were isolated and connected to linear actuators instrumented with load cells in series. During simulations, a force plate was moved relative to the stationary specimen through an inverse tibial kinematic path. Three-dimensional ankle and hindfoot kinematics were captured using a motion capture system. After ankle arthrodesis, kinematics were recorded using the same muscle force and kinematic inputs as the intact condition to determine how the hindfoot would behave when simulating normal gait. To assess the effect of ankle arthrodesis during simulated walking on adjacent joint kinematics, pre- and post-arthrodesis kinematics of the subtalar and talonavicular joint were directly compared along the stance phase and differences were assessed using two-tailed, paired Student’s t-tests with an alpha value set at p = 0.05. Results: Subtalar and talonavicular joint plantarflexion was greater during the early phase of stance in the ankle arthrodesis condition.(Figure 1B and 1C). Talonavicular joint motion also demonstrated greater dorsiflexion during late stance following ankle arthrodesis (Figure 1C). Ankle arthrodesis had no detectable effect on axial or coronal plane motion in adjacent joints of the hindfoot. Conclusion: This study reveals that sagittal plane motion in the hindfoot is increased following ankle arthrodesis. These results provide further insight into how motion is redistributed to adjacent joints after arthrodesis during gait. Such compensatory motions may be related to changes in contact mechanics in adjacent joints which can lead to degenerative changes.