Pizzari T, Kolt GS, Remedios L. Measurement of anterior-to-posterior translation of the glenohumeral joint using the KT-1000. JOSPT 1999;29:602-608.
The KT-1000 arthrometer is one of several instruments used to objectively measure the degree of knee translation with suspected anterior cruciate ligament deficiency. (Note: There is an arthrometer that can be placed in an autoclave, and thus can be used in the operating room post-surgery). No such instrument exists for measuring translation at the shoulder. These researchers slightly modified the KT-1000 and tested the shoulder for anterior-to-posterior (AP) translation of the humeral head.
The arm was tested in the scapular plane on 28 nonimpaired undergraduate university students. Test-retest reliability was good (ICC = 0.76) for the non-dominant shoulder and moderate (ICC = 0.67) for the dominant shoulder. For women, the nondominant shoulder range of translation was 23.8 mm +/- 4.2 mm; the dominant arm showed a translation of 22.6 mm +/-4.6 mm. For men, significantly less translation occurred. The nondominant shoulder demonstrated translation of 18.3 mm +/- 3.7 mm; the dominant shoulder demonstrated 17.1 mm +/- 3.7 mm.
What may be valuable as an extension of this study is for examiners to grade or predict translation on the subjects and compare arthrometer readings on the same subjects. Of course, testing on symptomatic versus asymptomatic subjects would also be of value to determine if pain or other factors influence the relaxation effect and therefore blunt findings.
Wang CH, McClure P, Pratt NE, Nobilini R. Stretching and strengthening exericses: their effect on three-dimensional scapular kinematics. Arch Phys Med Rehabil 1999;80:923-929.
These researchers evaluated the effect of shoulder strengthening and stretching on strength and scapular position. They measured scapular position using a three-dimensional electromechanical digitizer that determined both thoracic inclination and scapular orientation and position.
Twenty asymptomatic volunteers with a forward shoulder posture were given pectoral muscle stretching and resisted strengthening exercises for the scapular retractors and elevators and the glenohumeral abductors and external rotators. They performed the exercises and stretching three times per week for six weeks. Strength of horizontal abduction and internal and external rotation increased after exercise. More importantly, anterior inclination of the thoracic spine decreased and the glenohumeral contribution to elevation increased. At 90 degrees abduction, the scapula showed less upward rotation and less superior translation after the exercise test period.
The implications from this study are significant if taken together with the generally held belief that anterior impingement at the shoulder is influenced by scapular position; in particular, superior migration during abduction or other forms of elevation. The following study evaluates this connection by testing symptomatic versus asymptomatic patients with regard to scapular positioning.
Lukasiewicz AC, McClure P, Michener L, Pratt N, Sennett B. Comparison of three-dimensional scapular position and orientation between subjects with and without shoulder impingement. JOSPT 1999;29:574-586.
Twenty nonimpaired and 17 patients with impingement syndrome were tested to determine scapular position and orientation in three phases: arm at the side; elevated in the scapular plane to the horizontal; and maximum elevation. The instrument used to measure the scapular position was an electromechanical device that digitizes points in three dimensions (Metrocom, Faro Inc., Mary's Lake, FL). The digitizer uses a linkage arm comprised of six rotary potentiometers that are interfaced with a personal computer. The landmark points for determining scapular position and orientation included C7, T7, the root of the spine of the scapula, posterior angle of the acromion and inferior angle of the scapula. These points gave information regarding elevation and depression of the scapula superiorly and inferiorly in addition to tilting and rotation. They were then calculated as angles.
This study provided some interesting normative data in addition to comparative data between impingement syndrome patients and normal controls. Normative data for all subjects, regardless of whether in the impingement group or not, demonstrated that the scapula produced the following pattern with scapular plane elevation (scaption):
• increasing posterior tilt angle;
• increasing upward rotation angle;
• decreasing internal rotation angle.
The primary abnormal findings, demonstrated in the symptomatic shoulders of impingement syndrome patients, were less posterior tilting and excessive superior translation during scaption. The researchers speculate that this may contribute to impingement by decreasing suprahumeral space. They further propose that lack of posterior tilting may be due to either:
• tightness of the pectoralis minor muscle;
• lack of scapular mobility; or
• inadequate activity of the inferior portion of the serratus anterior.
They suggest that excessive superior translation may be due to:
• weakness of the intrinsic glenohumeral muscles such as the deltoid and rotator cuff; or
• capsular tightness (especially posterior capsular tightness).
Two other interesting findings from this study are:
• Both the symptomatic and asymptomatic sides of patients with impingement demonstrated more superior positions compared to nonim-paired subjects.
• Contrary to the popularly-held belief that decreased scapular upward rotation with elevation narrows the subacromial space in impingement patients, this study did not show a statistical difference with upward rotation between impingement patients versus nonimpaired subjects.
Some weaknesses of the study include the large degree of variability in the presentation of impingement patients and the number of subjects used. Increasing the testing group size and stratifying the impingement patients into different presentation groups would have increased the power and specificity of the study.