Yuki Tochigi

The Roles of Mechanical Stresses in the Pathogenesis of Osteoarthritis: Implications for Treatment of Joint Injuries*

Excessive joint surface loadings, either single (acute impact event) or repetitive (cumulative contact stress), can cause the clinical syndrome of osteoarthritis (OA). Despite advances in treatment of injured joints, the risk of OA following joint injuries has not decreased in the past 50 years. Cumulative excessive articular surface contact stress that leads to OA results from posttraumatic joint incongruity and instability, and joint dysplasia, but may also cause OA in patients without known joint abnormalities. In vitro investigations show that excessive articular cartilage loading triggers release of reactive oxygen species (ROS) from mitochondria, and that these ROS cause chondrocyte death and matrix degradation. Preventing release of ROS or inhibiting their effects preserves chondrocytes and their matrix. Fibronectin fragments released from articular cartilage subjected to excessive loads also stimulate matrix degradation; inhibition of molecular pathways initiated by these fragments prevents this effect. Additionally, injured chondrocytes release alarmins that activate chondroprogentior cells in vitro that propogate and migrate to regions of damaged cartilage. These cells also release chemokines and cytokines that may contribute to inflammation that causes progressive cartilage loss. Distraction and motion of osteoarthritic human ankles can promote joint remodeling, decrease pain, and improve joint function in patients with end-stage posttraumatic OA. These advances in understanding of how altering mechanical stresses can lead to remodeling of osteoarthritic joints and how excessive stress causes loss of articular cartilage, including identification of mechanically induced mediators of cartilage loss, provide the basis for new biologic and mechanical approaches to the prevention and treatment of OA.

The effect of accuracy of implantation on range of movement of the Scandinavian Total Ankle Replacement

When performing the Scandinavian Total Ankle Replacement (STAR), the positioning of the talar component and the selection of mobile-bearing thickness are critical. A biomechanical experiment was undertaken to establish the effects of these variables on the range of movement (ROM) of the ankle. Six cadaver ankles containing a specially-modified STAR prosthesis were subjected to ROM determination, under weight-bearing conditions, while monitoring the strain in the peri-ankle ligaments. Each specimen was tested with the talar component positions in neutral, as well as 3 and 6 mm of anterior and posterior displacement. The sequence was repeated with an anatomical bearing thickness, as well as at 2 mm reduced and increased thicknesses. The movement limits were defined as 10% strain in any ligament, bearing lift-off from the talar component or limitations of the hardware. Both anterior talar component displacement and bearing thickness reduction caused a decrease in plantar flexion, which was associated with bearing lift-off. With increased bearing thickness, posterior displacement of the talar component decreased plantar flexion, whereas anterior displacement decreased dorsiflexion.

Contribution of articular surface geometry to ankle stabilization

BACKGROUND Passive ankle stability under weight-bearing conditions has been found to depend substantially on the role of the articular surface geometry. In the present study, it was hypothesized that, in the ankle under axial loading, contact-stress changes in response to alterations of external load involve reproducible and specific patterns to maintain ankle stability. METHODS Six cadaver ankles with the peri-ankle ligaments intact were tested. Each specimen, held at several predetermined ankle positions under a primary one-body-weight axial force, was subjected to an additional secondary load. The secondary load-specifically, anterior/posterior shear force, inversion/eversion torque, or internal/external rotation torque-was applied independently, while motion associated with the two other secondary loading directions was unconstrained. Contact stress in the tibiotalar articulation was monitored by a real-time contact-stress sensor. Site-specific stress changes solely due to secondary loading at each load/position were identified by subtraction of the corresponding axial-force-only baseline distribution. The role of these stress changes in ankle stabilization was studied for each specimen by analyzing the data with a computer model of ankle geometry. RESULTS In the cadaver experiment, anterior and posterior shear forces caused reproducible positive changes in articular contact stresses on the anterior and posterior regions, respectively. Similar changes with version torques occurred on the medial and lateral regions. Positive changes with internal/external rotation torques occurred at two diagonal locations: anterolateral and posteromedial, or anteromedial and posterolateral. In the model analysis, these stress-change patterns were found to be effective in ankle stabilization, and the levels of contribution by the articular surface were calculated as accounting for approximately 70% of anterior/posterior stability, 50% of version stability, and 30% of internal/external rotation stability. CONCLUSIONS The documented changes in contact stress illustrate the major role of articular geometry in passive ankle stabilization. The levels of contribution by the articular surface that we calculated are consistent with those reported in the literature. These findings support the conceptual mechanism of ankle stabilization by redistribution of articular contact stress.

Talar Dome Access for Osteochondral Lesions

Background Recently, osteochondral grafting has become a popular procedure for treating challenging talar dome lesions. However, no guidelines exist for selection of the surgical approach to obtain perpendicular access to the talar dome. Hypothesis The majority of the talar dome can be accessed for perpendicular resurfacing procedures without need for osteotomy. Study Design Descriptive laboratory study. Methods Nine human cadaveric ankles were dissected in a standard fashion to expose the talar dome. Seven approaches were used, including 4 arthrotomies (anteromedial, anterolateral, posteromedial, and posterolateral) and 3 osteotomies (anterolateral [Chaput], distal fibula, and medial malleolar). The area available for perpendicular access to the dome was determined for each approach. Results On average, 17% (range, 10%-24%) of the medial talar dome and 20% (range, 16%-25%) of the lateral talar dome could not be accessed without osteotomy. On the lateral aspect of the superior talar dome surface, an anterolateral osteotomy adds a mean of 22% to sagittal plane exposure. Malleolar osteotomies, when performed using the method described, provide access to the entire medial and lateral sides; however, there remains a mean residual 15% (range, 11%-38%) of the central talar dome that cannot be accessed in a perpendicular manner with any approach. Conclusion Most of the talar dome can be accessed perpendicularly for resurfacing without malleolar osteotomy. Osteotomies substantially increase the access and are needed for extensive lesions. Part of the central portion of the talar dome is inaccessible to perpendicular resurfacing techniques with any standard approach. Clinical Relevance This study generated clear clinical guidelines to help decision making regarding the surgical approach to resurface the talar dome with osteochondral techniques. The majority of the talar dome can be accessed without osteotomy.

Ankle alignment on lateral radiographs. Part 1: sensitivity of measures to perturbations of ankle positioning.

Background: In ankles with end-stage osteoarthritis or with total ankle replacement (TAR), radiographic landmarks based on joint surface morphology usually are obscured and inadequate for radiographic measurement. Furthermore, because of difficulty in reproducibly positioning the ankle for a standing radiograph, any radiographic measure to accurately describe ankle alignment must tolerate perturbations of ankle positioning on clinical radiographs. To identify a radiographic measure of anteroposterior tibial-talar alignment that meets those requirements, three methods were compared to determine their sensitivity to perturbations in ankle positioning. Methods: Ten cadaver ankles had lateral radiographs taken in varying ankle positions in nine prespecified positions in the transverse plane and in seven positions in the sagittal plane. The anteroposterior tibial-talar alignment was quantified by three methods. Sensitivities to changes of ankle position in each plane were then compared. Results: With the tibial-axis-to-talus ratio (T-T ratio: the ratio into which the midlongitudinal axis of the tibial shaft divides the longitudinal talar length), sensitivity to ankle positional changes in either plane was lowest, with errors associated with 10 degrees of ankle malpositioning being 2.2%. The posterior-tibial-line-to-talus ratio (P-T ratio: a similar ratio, but using the posterior longitudinal line of the tibial shaft) showed higher sensitivity in the transverse plane than the T-T ratio, though the associated errors in either plane were nearly comparable. The tibial-axis-to-lateral-process distance (T-L distance: the perpendicular distance from the tibial axis to the tip of the lateral talar process) showed highest sensitivity in both planes. Conclusions: The T-T ratio tolerated perturbations of ankle positioning best among the tested measures. This measure is potentially applicable to clinical radiographic measurement when determining the anteroposterior tibial-talar alignment in ankles with articular degeneration or TAR. The P-T ratio also appears to have reasonable tolerance.

The Capsule’s Contribution to Total Hip Construct Stability – A Finite Element Analysis

Instability is a significant concern in total hip arthroplasty (THA), particularly when there is structural compromise of the capsule due to pre‐existing pathology or due to necessities of surgical approach. An experimentally grounded fiber‐direction‐based finite element model of the hip capsule was developed, and was integrated with an established three‐dimensional model of impingement/dislocation. Model validity was established by close similarity to results from a cadaveric experiment in a servohydraulic hip simulator. Parametric computational runs explored effects of graded levels of capsule thickness, of regional detachment from the capsules femoral or acetabular insertions, of surgical incisions of capsule substance, and of capsule defect repairs. Depending strongly upon the specific site, localized capsule defects caused varying degrees of construct stability compromise, with several specific situations involving over 60% decrement in dislocation resistance. Construct stability was returned substantially toward intact‐capsule levels following well‐conceived repairs, although the suture sites involved were often at substantial risk of failure. These parametric model results underscore the importance of retaining or robustly repairing capsular structures in THA, in order to maximize overall construct stability. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29:1642–1648, 2011

Ankle Alignment on Lateral Radiographs: Part 2: Reliability and Validity of Measures

Background: In ankles with end-stage osteoarthritis or after total ankle replacement (TAR), radiographic landmarks based on joint surface morphology usually are obscured and inadequate for measurement. Two methods for quantifying anteroposterior tibial-talar alignment without relying on those landmarks were identified in a corollary cadaver-based study. This study aimed to verify reliability and validity of those candidate measures. Methods: On clinical radiographs of 33 nonarthritic and 35 arthritic ankles, the anteroposterior tibial-talar alignment was quantified by the two methods; the tibial-axis-to-talus ratio (T-T ratio: the ratio into which the midlongitudinal axis of the tibial shaft divides the longitudinal talar length) and the posterior-tibial-line-to-talus ratio (P-T ratio: a similar ratio, but using the posterior longitudinal line along the tibial shaft). Two observers performed every measurement twice to evaluate intraobserver and interobserver reliability of the candidate measures. For nonarthritic ankles, the anteroposterior tibial-talar alignment was further determined by a control measure that directly quantified orientation of the talar dome relative to the tibial shaft. Correlation of the T-T and P-T ratios with the control measure was then evaluated for validity. Results: Measurement of the T-T ratio with arthritic ankles was highly reproducible with the coefficients of determination (R 2 ) greater than 0.95, for either interobserver or intraobserver. Correlation between this measure and the control measure was supported (R 2 = 0.60, p < 0.0001). Reliability of the P-T ratio also was strong (R 2 > 0.91), although both reliability and validity of this measure were relatively inferior to the T-T ratio. Conclusions: The T-T ratio reliably and validly described the anteroposterior tibial-talar alignment on clinical radiographs, regardless of the condition of ankle joint surface. This measure appears to be a reliable radiographic measure for determining the magnitude of anteroposterior talar subluxation in ankles with articular degeneration or after TAR and can facilitate clinical investigations.

Instability Dependency of Osteoarthritis Development in a Rabbit Model of Graded Anterior Cruciate Ligament Transection

BACKGROUND Joint instability has long been empirically recognized as a leading risk factor for osteoarthritis. However, formal mechanistic linkage of instability to osteoarthritis development has not been established. This study aimed to support a clinically accepted, but heretofore scientifically unproven, concept that the severity and rapidity of osteoarthritis development in unstable joints is dependent on the degree of instability. In a survival rabbit knee model of graded joint instability, the relationship between the magnitude of instability and the intensity of cartilage degeneration was studied at the organ level in vivo. METHODS Sixty New Zealand White rabbits received either complete or partial (medial half) transection of the anterior cruciate ligament or sham surgery (control) on the left knee. At the time that the animals were killed at eight or sixteen weeks postoperatively (ten animals for each treatment and/or test-period combination), the experimental knees were subjected to sagittal plane stability measurement, followed by whole-joint cartilage histological evaluation with use of the Mankin score. RESULTS Sagittal plane instability created in the partial transection group was intermediate between those in the complete transection and sham surgery groups. The partial and complete transection groups exhibited cartilage degeneration on the medial femoral and/or medial tibial surfaces. The average histological score (and standard deviation) for the medial compartment in the partial transection group (2.9 ± 0.9) was again intermediate, significantly higher than for the sham surgery group (1.9 ± 0.8) and significantly lower than for the complete transection group (4.5 ± 2.3). The average histological scores for the medial compartment in the partial transection group correlated significantly with the magnitude of instability, with no threshold effect being evident. The significance level of alpha was set at 0.05 for all tests. CONCLUSIONS The severity of cartilage degeneration increased continuously with the degree of instability in this survival rabbit knee model of graded instability.

THE ROLE OF THE INTEROSSEOUS TALOCALCANEAL LIGAMENT IN SUBTALAR JOINT STABILITY

Background: Injury of the interosseous talocalcaneal ligament (ITCL) has been recognized as a cause of subtalar instability, though lack of an accepted clinical test has limited the ability of clinicians to reliably make the diagnosis. Clinical effects of ITCL failure remain unclear because of insufficient understanding of the role of the ligament. Methods: Load-displacement characteristics of the subtalar joint were studied in six cadaver specimens using an axial distraction test and a transverse multi-direction drawer test. In all tests, cyclic loading (+/−60 N) was applied, and load-displacement responses were collected before and after sectioning of the ITCL. Two parameters were used to analyze the data: neutral-zone laxity as a measure of joint play, and flexibility as a measure of resistance to applied force. Results: In the axial distraction test, sectioning increased both neutral-zone laxity and flexibility (p = .01 and .02, respectively). In the transverse test, sectioning caused increase of both neutral-zone laxity and flexibility (p <.001, for each). Neutral-zone laxity increased most greatly along an axis defined roughly by the posterior aspect of the fibula and the central region of the medial malleolus. Flexibility increased most in the medial direction (p <.05, for each). Conclusions: Results confirmed the role of the ITCL in maintaining apposition of the subtalar joint, as well as suggested its role in stabilizing the subtalar joint against drawer forces applied to the calcaneus from lateral to medial. The dominant direction of increased neutral-zone laxity described above suggests the optimal direction for detecting subtalar instability involved with ITCL injury. Clinical Relevance: ITCL failure may result in subtalar instability and should be examined with a drawer force along the preferential axis roughly from the posterior aspect of the fibula to the central region of the medial malleolus. Further clinical evaluation is required to determine whether ITCL failure is reliably detectable.

Correlation of dynamic cartilage contact stress aberrations with severity of instability in ankle incongruity.

Joint instability is presumed to cause abnormality in cartilage contact mechanics, which accumulatively damages the articular surface, leading to osteoarthritis. The purpose of this study was to clarify the effect of instability on dynamic cartilage contact mechanics. Using human ankle cadaver specimens, potentially unstable ankles were modeled by introducing a coronally directed step‐off incongruity of the anterior tibial surface and/or by transecting the anterior talofibular ligament. Specimens were subjected to a duty cycle with quasi‐physiologic stance‐phase motion and loading. AP tibial forces were modulated, causing a controlled, quantifiable ankle subluxation during the duty cycle. Instantaneous changes in local articular contact stresses were continuously measured using a thin, flexible pressure transducer. Tests were repeated while varying the tibial surface condition (anatomic, 1‐mm step‐off, and 2‐mm step‐off), both before and after transection of the anterior talofibular ligament, with various AP force magnitudes, so that situations of various degrees of instability were created for each specimen. Instability events occurred when the step‐off incongruity was introduced, with the abnormality in joint kinematics being greater after ligament transection. Contact stress data revealed that these instability events involved distinctly abrupt increases/decreases in local articular contact stresses, and that the degree of abruptness was correlated nearly linearly with the abnormality in kinematics. The severity of contact stress aberration appeared to be correlated with the degree of instability. Given this linear relationship, even small instability events presumably involve appreciable abnormality in dynamic joint contact mechanics.