External rotation in the glenohumeral joint during elevation of the arm.

OBJECTIVE: To describe patterns of external rotation during humeral elevation, and to compare motion patterns.Design. Patterns of external rotation during forward flexion, scapular abduction and abduction in the frontal plane are described with P-spline curves with an approximately 95% confidence interval. BACKGROUND: External rotation of the humerus is an essential part of humeral elevation. Standard clinical assessment of external rotation provides insufficient information to describe external rotation patterns which may be essential for insight in shoulder disorders.Methods. The dominant and non-dominant arms of thirty subjects are measured, using a three-dimensional electromagnetic movement recording system. RESULTS: Overall group patterns demonstrate that humeral elevation in all planes is accompanied by about 55 degrees of external rotation, and each elevation plane has its own typical pattern. The dominant and non-dominant sides are comparable and can be combined. CONCLUSIONS: There are specific external rotation patterns for each elevation plane. Curves representing the approximately 95% confidence intervals make comparison between groups possible. This method can therefore possibly be used to study the external rotation patterns in groups with certain shoulder disorders to evaluate the results of before and after treatment. RELEVANCE: The method presented in this paper can be used to study external rotation patterns in healthy shoulders and in shoulders with a specific disorders to gain more insight, to define functional treatment, and to evaluate the results of treatment.

The kinematic elbow axis as a parameter to evaluate total elbow replacement: A cadaver study of the iBP elbow system.

Malpositioning of prosthetic implants leads to biomechanical changes, often resulting in deteriorating functional outcome. This emphasizes the relevance of evaluating the surgical process of inserting the prostheses. This study tested to what extent the iBP elbow prosthesis and its alignment tools enabled a surgeon to reconstruct normal joint kinematics. It demonstrates the use of the kinematic elbow axis as an evaluation tool. An electromagnetic tracking device registered controlled passive elbow flexion of 10 embalmed upper extremities. The position and direction of the preoperative and postoperative kinematic elbow axes were established with the use of helical axes and compared. The postoperative position of the elbow axis differed from the preoperative axis because of limitations of the alignment tools. Suggestions for adjustment of the alignment tools are made. The direction of the imposed resection plane was correct; therefore, the direction of the postoperative elbow axis corresponded with the direction of the preoperative axis.

Patterns of loosening of the glenoid component.

The incidence of loosening of a cemented glenoid component in total shoulder arthroplasty, detected by means of radiolucent lines or positional shift of the component on true anteroposterior radiographs, has been reported to be between 0% and 44%. Radiolucent lines are, however, difficult to detect and to interpret because of the mobility of the shoulder girdle and the obliquity of the glenoid which hinder standardisation of radiographs. We examined radiolucencies around cemented glenoid components in 48 patients, with a mean follow-up of 5.3 years, and found progressive changes to be present predominantly at the inferior pole of the component. This may hold a clue for the mechanism of loosening of this implant. In five patients we performed an additional analysis of loosening of the glenoid component using digital roentgen stereophotogrammetric analysis (RSA). After three years, three of the five implants had loosened (migration 1.2 to 5.5 mm). In only one, with gross loosening, were the radiological signs consistent with the RSA findings. When traditional radiographs are used for assessment, the rate of early loosening is underestimated. We recommend that RSA be used for this.

Measurement of three dimensional shoulder movement patterns with an electromagnetic tracking device in patients with a frozen shoulder.

OBJECTIVE: To compare three dimensional movement patterns of the affected and non-affected shoulder in patients with a frozen shoulder before and after physical therapy. METHODS: Patients with a unilateral frozen shoulder were assessed before and after three months of treatment. Three dimensional movement analysis was performed with the "Flock of Birds" electromagnetic tracking device while the patient raised their arms in three directions. Slopes of the regression lines of glenohumeral joint rotation versus scapular rotation, reflecting the scapulohumeral rhythm, were calculated. All assessments were made for both the affected and the unaffected side. Additional assessments included conventional range of motion (ROM) measurements and visual analogue scales (VAS) (0-100 mm) for shoulder pain at rest, during movement, and at night. RESULTS: Ten patients with a unilateral frozen shoulder were included. The slopes of the curves of the forward flexion, scapular abduction, and abduction in the frontal plane of the affected and the unaffected side were significantly different in all three movement directions. Mean differences were 0.267, 0.215, and 0.464 (all p values <0.005), respectively. Mean changes of the slopes of the affected side after treatment were 0.063 (p=0.202), 0.048 (p=0.169), and 0.264 (p=0.008) in forward flexion, scapular abduction, and abduction in the frontal plane, respectively. All patients showed significant improvement in active ROM (all p<0.005), and the VAS for pain during movement and pain at night (p<0.05). CONCLUSIONS: With a three dimensional electromagnetic tracking system the abnormal movement pattern of a frozen shoulder, characterised by the relatively early laterorotation of the scapula in relation to glenohumeral rotation during shoulder elevation, can be described and quantified. Moreover, the system is sufficiently sensitive to detect clinical improvements. Its value in other shoulder disorders remains to be established.

The glenohumeral joint rotation centre in vivo.

Within the framework of the current call for standardization in upper extremity research, three methods to determine the glenohumeral joint rotation centre in vivo were tested. Therefore, subjects performed humeral movements, while a 3D electromagnetic tracking device registered the motion of the humerus with respect to the scapula. For the first method to estimate the glenohumeral joint rotation centre five scapular bony landmarks served as input to regression equations. The second method fitted a sphere through the humeral position data and the third method calculated the rotation centre determining an optimal helical axis. The experiment consisted of two parts, at first one subject was measured 10 times, subsequently one observer measured 10 subjects twice and another observer measured these subjects once. The first part of the experiment demonstrated that all methods are capable to reproduce the rotation centre within 4mm, but the location of the centre differed significantly between methods (p<0.001). The second part, showed that inter- and intra-observer reliability was sufficiently for the sphere-fitting method and for the helical-axes method. The two observations of one observer differed significantly (p<0.008) using the regression method. The authors prefer the helical-axes method, it is a reliable and valid method which can be applied in movement registration of healthy subjects and patients with a shoulder endoprosthesis, it can be applied in hinge joints to determine a rotation axis instead of a rotation centre which is desirable in standardized upper extremity research, and calculation time is short.

Determining the optimal flexion-extension axis of the elbow in vivo - a study of interobserver and intraobserver reliability.

In the current study the interobserver and intraobserver reliability of a recently developed method to obtain the position and orientation vectors of the flexion-extension axis of the elbow in vivo is determined. The method uses the Flock of Birds six degrees-of-freedom electromagnetic tracking device. Ten subjects performed three trials comprising five flexion and extension cycles. The movements of the forearm with respect to the upper arm were recorded. Observer A measured two trials and observer B measured one trial. Optimal instantaneous helical axes were calculated in a humeral coordinate system for each trial. Intraclass correlation coefficients and 99% confidence intervals were computed to compare the three measurements. Zero was in the range of all the narrow confidence intervals, which is strong indication for resemblance. Interobserver intraclass correlation coefficients values for orientation vectors were good to excellent and intraobserver values were fair to good. The intraclass correlation coefficients values for position vectors were lower, probably due to the lack of variance between subjects. It is concluded that the method is reliable and can be used in certain clinical settings.

Predicting mechanical load of the glenohumeral joint, using net joint moments.

OBJECTIVE: To evaluate the relationship between net moments for the glenohumeral joint as calculated with a model that is easy to apply (Static Strength Prediction Program (SSPP)) and the internal forces, calculated with a simulation model of the human shoulder (Delft Shoulder Model, DSM). DESIGN: Static recordings of bony landmarks of the shoulder girdle during prescribed arm motions using a three-dimensional (3D) digitizer. BACKGROUND: The SSPP is a biomechanical model for the evaluation of workload. Concerning the shoulder the output of the model consists of net moments in the glenohumeral joint. For the glenohumeral joint the relationship between net joint moments and internal load predictions is unknown, therefore it is useful to investigate whether the SSPP can be used to predict mechanical load in the glenohumeral joint. METHODS: 3D co-ordinates of bony landmarks of the shoulder girdle are recorded, in variable arm positions, in four different planes. RESULTS: A strong linear relationship between compression forces and net moments is found, which makes it reasonable to assume a direct relationship between net moments and joint compression forces. CONCLUSIONS: (a) Net joint moments appeared to be a good indicator for mechanical load in the glenohumeral joint in static situations. (b) The SSPP can be used to predict these joint moments for static situations. RELEVANCE: biomechanical models predicting mechanical load can be used in work situations in order to prevent overload and injuries, as well as in many other areas, for instance to evaluate the mechanical load during wheelchair propulsion.

Determination of the optimal elbow axis for evaluation of placement of prostheses.

OBJECTIVE: To present a method to determine the position and orientation of the mean optimal flexion axis of the elbow in vivo to be used in clinical research. DESIGN: Registering the movements of the forearm with respect to the upper arm during five cycles of flexion and extension of the elbow using a 6 degrees-of-freedom electromagnetic tracking device. BACKGROUND: Loosening of elbow endoprostheses could be caused by not placing the prostheses in a biomechanically optimal way. To evaluate the placement of endoprostheses with regard to loosening, a method to determine the elbow axis is needed. METHODS: The movements of the right forearm with respect to the upper arm during flexion and extension were registered with a 6 degrees-of-freedom electromagnetic tracking device. A mean optimal instantaneous helical axis of 10 elbows was calculated in a coordinate system related to the humerus. RESULTS: The average position of the flexion/extension axis was 0.81 cm (SD 0.66 cm) cranially and 1.86 cm (SD 0.72 cm) ventrally of the epicondylus lateralis. The average angle with the frontal plane was 15.3 degrees (SD 2 degrees). CONCLUSIONS: A useful estimation of the position and orientation of a mean optimal flexion axis can be obtained in vivo.