Introduction

The Stanmore Percentage of Normal Shoulder Assessment (SPONSA) is a simple, fast and reproducible measure of the subjective state of a shoulder. It has been invaluable in our busy clinical practice. This study validates the SPONSA score against the Oxford Shoulder and Constant score and demonstrates a greater sensitivity to change.

This pilot study assesses level of agreement between surface and fine wire electromyography (EMG), in order to establish if surface is as reliable as fine wire in the diagnosis and treatment of abnormal muscle patterning in the shoulder. 18 subjects (11 female, mean 36 years) with unstable shoulders were recruited after written consent and ethical approval. Anthropometric information and mean skinfold size for triceps, subscapular, biceps and suprailiac sites were obtained. Triple stud self adhesive surface electrodes (“Triode” – Thermo Scientific) were placed over Pectoralis Major (PM), Latissimus Dorsi (LD), Anterior Deltoid (AD) and Infraspinatus (IS) at standardised locations. A ‘Medi-Link’ dual channel surface EMG (Electro Medical Supplies) displayed a rectified smoothed signal. Patients performed five identical uniplanar standard movements (flexion, abduction, external rotation, extension and cross body adduction). After a rest period, a dual needle technique for fine wire insertion was used displaying a raw EMG signal on a ‘Sapphire II’ four channel EMG unit. An experienced examiner in each technique reported if muscle activation patterns differed from agreed normal during any movement and were blinded to the other test results. Sensitivity, specificity and kappa values for level of agreement between methods were calculated for each muscle according to the method of Altman. 15 patients were successfully tested. Sensitivity, specificity and kappa values between techniques for each muscles were PM (57%, 50%, 0.07), LD (38%, 85%, 0.22), AD (0%, 76%, −0.19) and IS (85%, 75%, 0.6). Only IS demonstrated high sensitivity and specificity and a moderate level of agreement between the two techniques. There was no correlation between skinfold size and agreement levels. Surface did not agree with wire analysis for PM, LD and AD, although IS did show moderate agreement. Subcutaneous fat did not appear to affect correlation.

This study identifies variations in presentation and demographics between structural and non-structural (muscle patterning) shoulder instability.

We analysed 1020 unstable shoulders (855 patients) from our institution database. Demographic details, direction and aetiology were obtained from medical records. Anterior dislocations comprised 67%, posterior 31% and inferior 2% of all directions of instability and 75 shoulders had multidirectional instability.

Structural causes were dominant in anterior instability (traumatic 39% and atraumatic 38%) and muscle patterning in posterior (81%) and inferior (90%) instability. Males accounted for 64% of all patients (73% of all structural patients and 53% of muscle patterning patients. Mean age at presentation was 25 years old (structural patients 28 years and muscle patterning patients 21 years old). There were 690 unilaterally unstable shoulders (57% right- and 43% left-sided); the dominant arm was affected in 58% overall, in 42% of all left-handers and only 33% of left-handers with muscle patterning. Bilateral shoulder instability occurred in 19% of all patients (12% of patients with structural instability and 28% of those with muscle patterning instability). For muscle patterning, the mean age at onset of symptoms was 14 years, and mean length of symptoms before presentation was 8 years. There was a trimodal distribution of age at onset of symptoms corresponding to peaks at 6, 14 and 20 years. In the group with onset of muscle patterning under 10 years old, there was a higher proportion of females (71% vs 47%), laxity (63% vs 29%) and bilaterality (54% vs 42%), and fewer presenting with pain (17% vs 50%).

Muscle patterning instability is associated with a demographic and presentation profile which may help distinguish it from structural forms of instability. As age at presentation increased, pain increased and joint laxity decreased. Bilaterality did not appear to be associated with gender, the presence of laxity or pain.

This study identifies variations in presentation and demographics for different forms of shoulder instability. We analysed 1020 unstable shoulders (855 patients) from a previously presented database. Demographic details, direction and aetiology were obtained from medical records. Anterior dislocations comprised 67%, posterior 31% and inferior 2% of all directions of instability and 75 shoulders had multidirectional instability. Structural causes were dominant in anterior instability (traumatic 39% and atraumatic 38%) and muscle patterning in posterior (81%) and inferior (90%) instability. Males accounted for 64% of all patients (73% of all structural patients and 53% of muscle patterning patients. Mean age at presentation was 25 years old (structural patients 28 years and muscle patterning patients 21 years old). There were 690 unilaterally unstable shoulders (57% right- and 43% left-sided); the dominant arm was affected in 58% overall, in 42% of all left-handers and only 33% of left-handers with muscle patterning. Bilateral shoulder instability occurred in 19% of all patients (12% of patients with structural instability and 28% of those with muscle patterning instability). For muscle patterning, the mean age at onset of symptoms was 14 years, and mean length of symptoms before presentation was 8 years. There was a trimodal distribution of age at onset of symptoms corresponding to peaks at 6, 14 and 20 years. In the group with onset of muscle patterning under 10 years old, there was a higher proportion of females (71% vs 47%), laxity (63% vs 29%) and bilaterality (54% vs 42%), and fewer presenting with pain (17% vs 50%). As age at presentation increased, pain increased and joint laxity decreased. Bilaterality did not appear to be associated with gender, the presence of laxity or pain. Muscle patterning instability is associated with a demographic and presentation profile which may help distinguish it from structural forms of instability.

We present the use of dynamic electromyographic analysis (DEMG) in the diagnosis of muscle patterning instability. DEMG’s were requested in 168 of 562 muscle patterning shoulders with suspected subclinical or clinically complex muscle patterning instability. An experienced neurophysiologist (blinded to the clinical findings and direction of instability) inserted dual-wire tungsten electrodes into pectoralis major, latissimus dorsi, infraspinatus and anterior deltoid. Muscle activity was recorded during rest, flexion, abduction, extension, and cross-body adduction. 5 investigations were abandoned. The timing and magnitude of muscle activity was noted and compared to the clinical diagnosis and direction of instability. DEMG identified a total of 204 abnormal muscle patterns in 163 shoulders. The examination was normal in 13 patients (8%). A single muscle was abnormal in 63 shoulders, 2 muscles in 55, 3 muscles in 9, and all 4 muscles in one shoulder. Over-activation of pectoralis major was identified in 58%, and latissimus dorsi in 70%, of shoulders with anterior instability. In posterior instability, latissimus dorsi was overactive in 76%, anterior deltoid in 14% and infraspinatus was under-active in 24%. Pectoralis major and Latissimus dorsi were both overactive in 38% of anterior, 29% of posterior and 38% of multidirectional instability. Abnormal muscle patterns were identified in 52 shoulders with subclinical muscle patterning. A further 98 shoulders had 134 clinically abnormal muscle patterns. These were confirmed by DEMG in 57 cases (sensitivity 43%), and DEMG’s were normal in 77 (specificity 43%). DEMG also identified 65 additional muscles as abnormal in the 98 clinically abnormal shoulders. DEMG performed by an experienced neurophysiologist provides additional information regarding abnormal muscle activation in selected complex or subtle cases of muscle patterning instability in which clinical examination has a low sensitivity and specificity.

Aim: To demonstrate that inappropriate sequencing of activation of shoulder muscles can cause shoulder instability.

Methods. The records of 933 cases of recurrent shoulder instability referred to a specialist shoulder service between 1993 and 2003 were reviewed. All patients were assessed clinically. Muscle patterning abnormality (Bayley 1986) was identified in 428 patients (46%). Confirmatory functional electromyography was performed in 166 (36%). Inappropriate pectoralis major activation was identified in 73% of anterior instability. In posterior instability, inappropriate activation of latissimus dorsi and anterior deltoid was present in 72% and infra-spinatus was suppressed in 19%. Arthroscopic assessment was performed in 141 (33%), identifying structural lesions of instability in 86 (20%).

All patients diagnosed with muscle patterning disorder received specilalist physical therapy using biofeedback. Symptomatic improvement or stability was achieved in 76% of patients with anterior instability but with no previous surgery, and in 53% of patients with previous surgery. Posterior instability was eliminated in 85% of cases.

Conclusion. Muscle patterning abnormalities contribute to recurrent instability of the shoulder in 46% of cases. The success of physical therapy in these patients is high.