Carrie A. Voycheck

Altered tibiofemoral joint contact mechanics and kinematics in patients with knee osteoarthritis and episodic complaints of joint instability

BACKGROUND To evaluate knee joint contact mechanics and kinematics during the loading response phase of downhill gait in knee osteoarthritis patients with self-reported instability. METHODS Forty-three subjects, 11 with medial compartment knee osteoarthritis and self-reported instability (unstable), 7 with medial compartment knee osteoarthritis but no reports of instability (stable), and 25 without knee osteoarthritis or instability (control) underwent Dynamic Stereo X-ray analysis during a downhill gait task on a treadmill. FINDINGS The medial compartment contact point excursions were longer in the unstable group compared to the stable (P=0.046) and the control groups (P=0.016). The peak medial compartment contact point velocity was also greater for the unstable group compared to the stable (P=0.047) and control groups (P=0.022). Additionally, the unstable group demonstrated a coupled movement pattern of knee extension and external rotation after heel contact which was different than the coupled motion of knee flexion and internal rotation demonstrated by stable and control groups. INTERPRETATION Our findings suggest that knee joint contact mechanics and kinematics are altered during the loading response phase of downhill gait in knee osteoarthritis patients with self-reported instability. The observed longer medial compartment contact point excursions and higher velocities represent objective signs of mechanical instability that may place the arthritic knee joint at increased risk for disease progression. Further research is indicated to explore the clinical relevance of altered contact mechanics and kinematics during other common daily activities and to assess the efficacy of rehabilitation programs to improve altered joint biomechanics in knee osteoarthritis patients with self-reported instability.

A Biomechanical Perspective on Physical Therapy Management of Knee Osteoarthritis

SYNOPSIS Altered knee joint biomechanics and excessive joint loading have long been considered as important contributors to the development and progression of knee osteoarthritis. Therefore, a better understanding of how various treatment options influence the loading environment of the knee joint could have practical implications for devising more effective physical therapy management strategies. The aim of this clinical commentary was to review the pertinent biomechanical evidence supporting the use of treatment options intended to provide protection against excessive joint loading while offering symptomatic relief and functional improvements for better long-term management of patients with knee osteoarthritis. The biomechanical and clinical evidence regarding the effectiveness of knee joint offloading strategies, including contralateral cane use, laterally wedged shoe insoles, variable-stiffness shoes, valgus knee bracing, and gait-modification strategies, within the context of effective disease management is discussed. In addition, the potential role of therapeutic exercise and neuromuscular training to improve the mechanical environment of the knee joint is considered. Management strategies for treatment of joint instability and patellofemoral compartment disease are also mentioned. Based on the evidence presented as part of this clinical commentary, it is argued that special considerations for the role of knee joint biomechanics and excessive joint loading are necessary in designing effective short- and long-term management strategies for treatment of patients with knee osteoarthritis. LEVEL OF EVIDENCE Therapy, level 5.

A Method for Predicting Collagen Fiber Realignment in Non-Planar Tissue Surfaces as Applied to Glenohumeral Capsule During Clinically Relevant Deformation

Previously developed experimental methods to characterize micro-structural tissue changes under planar mechanical loading may not be applicable for clinically relevant cases. Such limitation stems from the fact that soft tissues, represented by two-dimensional surfaces, generally do not undergo planar deformations in vivo. To address the problem, a method was developed to directly predict changes in the collagen fiber distribution of nonplanar tissue surfaces following 3D deformation. Assuming that the collagen fiber distribution was known in the un-deformed configuration via experimental methods, changes in the fiber distribution were predicted using 3D deformation. As this method was solely based on kinematics and did not require solving the stress balance equations, the computational efforts were much reduced. In other words, with the assumption of affine deformation, the deformed collagen fiber distribution was calculated using only the deformation gradient tensor (obtained via an in-plane convective curvilinear coordinate system) and the associated un-deformed collagen fiber distribution. The new method was then applied to the glenohumeral capsule during simulated clinical exams. To quantify deformation, positional markers were attached to the capsule and their 3D coordinates were recorded in the reference position and three clinically relevant joint positions. Our results showed that at 60deg of external rotation, the glenoid side of the posterior axillary pouch had significant changes in fiber distribution in comparison to the other sub-regions. The larger degree of collagen fiber alignment on the glenoid side suggests that this region is more prone to injury. It also compares well with previous experimental and clinical studies indicating maximum principle strains to be greater on the glenoid compared to the humeral side. An advantage of the new method is that it can also be easily applied to map experimentally measured collagen fiber distribution (obtained via methods that require flattening of tissue) to their in vivo nonplanar configuration. Thus, the new method could be applied to many other nonplanar fibrous tissues such as the ocular shell, heart valves, and blood vessels.

Effects of region and sex on the mechanical properties of the glenohumeral capsule during uniaxial extension

Surgical repair of the glenohumeral capsule after dislocation ignores regional boundaries of the capsule and is not sex specific. However, each region of the capsule functions to stabilize the joint in different positions, and differences in joint laxity between men and women have been found. The objectives of this research were to determine the effects of region (axillary pouch and posterior capsule) and sex on the material properties of the glenohumeral capsule. Boundary conditions derived from experiments were used to create finite-element models that applied tensile deformations to tissue samples from the capsule. The material coefficients of a hyperelastic constitutive model were determined via inverse finite-element optimization, which minimized the difference between the experimental and finite-element model-predicted load-elongation curve. These coefficients were then used to create stress-stretch curves representing the material properties of the capsule regions for each sex in response to uniaxial extension. For the axillary pouch, the C1 (men: 0.28+/-0.39 MPa and women: 0.23+/-0.12 MPa) and C2 (men: 8.2+/-4.1 and women: 7.7+/-3.0) material coefficients differed between men and women by only 0.05 MPa and 0.5, respectively. Similarly, the posterior capsule coefficients differed by 0.15 MPa (male: 0.49+/-0.26 MPa and female: 0.34+/-0.20 MPa) and 0.6 (male: 7.8+/-2.9 and female: 7.2+/-3.0), respectively. No differences could be detected in the material coefficients between regions or sexes. As a result, surgeons may not need to consider region- and sex-specific surgical repair techniques. Furthermore, finite-element models of the glenohumeral joint may not need region- or sex-specific material coefficients when using this constitutive model.

Knee joint contact mechanics during downhill gait and its relationship with varus/valgus motion and muscle strength in patients with knee osteoarthritis☆

OBJECTIVE The objective of this exploratory study was to evaluate tibiofemoral joint contact point excursions and velocities during downhill gait and assess the relationship between tibiofemoral joint contact mechanics with frontal-plane knee joint motion and lower extremity muscle weakness in patients with knee osteoarthritis (OA). METHODS Dynamic stereo X-ray was used to quantify tibiofemoral joint contact mechanics and frontal-plane motion during the loading response phase of downhill gait in 11 patients with knee OA and 11 control volunteers. Quantitative testing of the quadriceps and the hip abductor muscles was also performed. RESULTS Patients with knee OA demonstrated larger medial/lateral joint contact point excursions (p < 0.02) and greater heel-strike joint contact point velocities (p < 0.05) for the medial and lateral compartments compared to the control group. The peak medial/lateral joint contact point velocity of the medial compartment was also greater for patients with knee OA compared to their control counterparts (p = 0.02). Additionally, patients with knee OA demonstrated significantly increased frontal-plane varus motion excursions (p < 0.01) and greater quadriceps and hip abductor muscle weakness (p = 0.03). In general, increased joint contact point excursions and velocities in patients with knee OA were linearly associated with greater frontal-plane varus motion excursions (p < 0.04) but not with quadriceps or hip abductor strength. CONCLUSION Altered contact mechanics in patients with knee OA may be related to compromised frontal-plane joint stability but not with deficits in muscle strength.

Changes to the mechanical properties of the glenohumeral capsule during anterior dislocation

The glenohumeral joint is the most frequently dislocated major joint in the body, and instability due to permanent deformation of the glenohumeral capsule is a common pathology. The corresponding change in mechanical properties may have implications for the ideal location and extent of plication, which is a common clinical procedure used to repair the capsule. Therefore, the objective of this study was to quantify the mechanical properties of four regions of the glenohumeral capsule after anterior dislocation and compare the properties to the normal glenohumeral capsule. Six fresh-frozen cadaveric shoulders were dislocated in the anterior direction with the joint in the apprehension position using a robotic testing system. After dislocation, mechanical testing was performed on the injured glenohumeral capsule by loading the tissue samples in tension and shear. An inverse finite element optimization routine was used to simulate the experiments and obtain material coefficients for each tissue sample. Cauchy stress-stretch curves were then generated to represent the mechanical response of each tissue sample to theoretical loading conditions. Based on several comparisons (average of the material coefficients, average stress-stretch curve for each region, and coefficients representing the average curves) between the normal and injured tissue samples, the mechanical properties of the injured tissue samples from multiple regions were found to be lower than those of the normal tissue in tension but not in shear. This finding indicates that anterior dislocation primarily affects the tensile behavior of the glenohumeral capsule rather than the shear behavior, and this phenomenon could be caused by plastic deformation of the matrix, permanent collagen fiber rotation, and/or collagen fiber failure. These results suggest that plication and suturing may not be sufficient to return stability to the shoulder after dislocation in all individuals. Thus, surgeons may need to perform a procedure that reinforces or stiffens the tissue itself, such as reconstruction or augmentation, to improve repair procedures.

Injury to the Glenohumeral Capsule During Anterior Dislocation Results in Damage to the Anteroinferior Capsule

The glenohumeral joint is the most frequently dislocated major joint in the body with about 2% of the population dislocating their shoulders between the ages of 18 and 70 [1]. About 80% of these shoulder dislocations occur in the anterior direction, and they most commonly occur in the apprehension position, which is characterized by 60° of glenohumeral abduction and 60° of external rotation [2]. The most common pathology associated with dislocation is instability due to permanent deformation [3]. Current surgical repair techniques for shoulder dislocations are inadequate with about 25% of patients still experiencing pain and instability after surgery [4]. By assessing the strain distribution, it is possible to determine the stabilizing function of the various capsular regions. In addition, surgeons could benefit from knowing the location and extent of tissue damage when placating the capsule during repair procedures. Therefore, the objective of this study was to determine the location and extent of injury to the anteroinferior capsule during anterior dislocation by quantifying the strain at dislocation and the non-recoverable strain following dislocation.Copyright

Collagen Fiber Alignment and Maximum Principal Strain in the Glenohumeral Capsule Predict Location of Failure During Uniaxial Extension

The glenohumeral joint is frequently dislocated causing injury to the glenohumeral capsule (axillary pouch (AP), anterior band of the inferior glenohumeral ligament (AB-IGHL), posterior band of the inferior glenohumeral ligament (PB-IGHL), posterior (Post), and anterosuperior region (AS)). [1, 2] The capsule is a passive stabilizer to the glenohumeral joint and primarily functions to resist dislocation during extreme ranges of motion. [3] When unloaded, the capsule consists of randomly oriented collagen fibers, which play a pertinent role in its function to resist loading in multiple directions. [4] The location of failure in only the axillary pouch has been shown to correspond with the highest degree of collagen fiber orientation and maximum principle strain just prior to failure. [4, 5] However, several discrepancies were found when comparing the collagen fiber alignment between the AB-IGHL, AP, and PB-IGHL. [3,6,7] Therefore, the objective was to determine the collagen fiber alignment and maximum principal strain in five regions of the capsule during uniaxial extension to failure and to determine if these parameters could predict the location of tissue failure. Since the capsule functions as a continuous sheet, we hypothesized that maximum principal strain and peak collagen fiber alignment would correspond with the location of tissue failure in all regions of the glenohumeral capsule.Copyright

Changes in Capsule Function Following Anterior Dislocation Elucidate the Need for Standardized Clinical Exams to Diagnose Shoulder Instability

The anteroinferior glenohumeral capsule (anterior band of the inferior glenohumeral ligament (AB-IGHL), axillary pouch) limits anterior translation, particularly in positions of external rotation, and as a result is frequently injured during anterior dislocation. [1,2] A common capsular injury is permanent tissue deformation, however, the extent and effects of this injury are difficult to evaluate as the deformation cannot be seen using diagnostic imaging. In addition, clinical exams to diagnose this injury are not reliable [3] and poor patient outcome still exists following repair procedures. [4] Previous experimental models have observed increased joint mobility following permanent tissue deformation. [5] While other models have quantified the permanent deformation using nonrecoverable strain [6], no model has correlated the amount of tissue damage to altered capsule function. Understanding the relationship between the extent of tissue damage and changes in capsule function following anterior dislocation could aid surgeons in diagnosing and treating anterior instability. Therefore, the objectives of this work were to 1) quantify the nonrecoverable strain in the anteroinferior capsule resulting from an anterior dislocation and 2) evaluate capsule function (strain distribution in anteroinferior capsule, anterior translation) during a simulated clinical exam at three joint positions, in the intact and injured joint.Copyright

Injury to the Glenohumeral Capsule During Anterior Dislocation Leads to Higher Joint Contact Forces During Simulated Clinical Exams

Glenohumeral joint stability is maintained by a combination of active and passive soft tissue structures and osteoarticular contact. Anatomical structures that contribute to each of these categories include the rotator cuff muscles, the glenohumeral capsule, and the contact between the articular surfaces of the humeral head and glenoid of the scapula, respectively. Dislocation may result in injury to one or more of these stabilizing components requiring the other structures to account for the deficit. For example, previous research has shown that a torn supraspinatus tendon results in increased bony contact forces during glenohumeral abduction. [1] Another common injury resulting from dislocation is permanent deformation of the glenohumeral capsule as the capsule is the primary static restraint to anterior translation in positions of external rotation. [2] Increased joint translations and rotations usually occur following permanent deformation [3] indicating a loss in joint stability provided by the capsule. These changes in joint kinematics following dislocation imply that differences in the contact forces between the humerus and scapula may exist as well. Irregular contact between two articular surfaces can lead to abnormal wear and an increased risk of osteoarthritis when left untreated. Therefore, the objective of this work was to assess the affect of anterior dislocation on glenohumeral joint stability by determining the in situ force in the glenohumeral capsule and the bony contact forces between the humerus and scapula during a simulated clinical exam at three joint positions in the intact and injured joint.Copyright