Shoulder subluxation in hemiplegia: effects of three different supports

Shoulder subluxation in hemiplegia is a difficult problem to manage and it may be associated with pain and other complications. Measurements taken from x-rays have been used to obtain objective measures of shoulder subluxation, but have not been used to compare the effects of different shoulder supports. This study used x-ray measurements to evaluate different shoulder supports for subluxation in hemiplegia and to see if there was a significant difference between the Harris hemisling and the Bobath sling. The Harris hemisling gave good vertical correction of subluxation and compared closely to the uninvolved shoulder. The Bobath sling did not correct the subluxation as well, and the mean difference between the two slings was significant. The arm trough or lap board was less effective and tended to overcorrect. The Harris hemisling and arm trough or lap board had horizontal measurements similar to the uninvolved shoulders. The Bobath sling, however, distracted the glenohumeral joint horizontally and was more variable. The mean horizontal difference between the Harris hemisling and the Bobath sling was significant. These results support the effectiveness and specificity of shoulder support to decrease subluxation after hemiplegia.     

Glenohumeral joint subluxation and reflex sympathetic dystrophy in hemiplegic patients

OBJECTIVE: To examine the relation between glenohumeral joint subluxation and reflex sympathetic dystrophy (RSD) in hemiplegic patients. DESIGN: Case-control study. SETTING: Inpatient rehabilitation hospital. PATIENTS: Thirty-five hemiplegic patients with RSD (RSD group) and 35 hemiplegic patients without RSD (non-RSD group) were included in the study. Patients with rotator cuff rupture, brachial plexus injury, or spasticity greater than stage 2 on the Ashworth scale were excluded. MAIN OUTCOME MEASURES: Both the RSD and non-RSD groups were assessed for presence and grade of subluxation from radiographs using a 5-point categorization. The degree of shoulder pain of the non-RSD group was assessed by a visual analogue scale of 10 points. RESULTS: Glenohumeral subluxation was found in 74.3% of the RSD and 40% of the non-RSD group (p = .004). In the non-RSD group, 78.6% of the patients with subluxation and 38.1% of the patients without subluxation reported shoulder pain (p = .019). No correlation was found between the degree of shoulder pain and grade of subluxation in the non-RSD group (p = .152). CONCLUSION: Findings from this study suggest that shoulder subluxation may be a causative factor for RSD. Therefore, prevention and appropriate treatment of glenohumeral joint subluxation should be included in rehabilitation of hemiplegic patients.     

Physical Medicine and Rehabilitation (85)

Glenohumeral joint subluxation and reflex sympathetic dystrophy in hemiplegic patients. (Kocaeli University, Kocaeli, Turkey) Arch Phys Med Rehabil 1999; 81:944–946. This is a case‐controlled study of the relationship between glenohumeral joint subluxation and reflex sympathetic dystrophy (RSD) in hemiplegic patients set in an inpatient rehabilitation hospital. Thirty‐five hemiplegic patients with RSD (RSD group) and 35 hemiplegic patients without RSD (non‐RSD group) were included in this study. Patients with rotator cuff rupture, brachial plexus injury, or spasticity greater than stage 2 on the Ashworth scale were excluded. Both the RSD and non‐RSD groups were assessed for presence and grade of subluxation from radiographs using a 5‐point categorization. The degree of shoulder pain of the non‐RSD group was assessed by a visual analogue scale of 10 points. Glenohumeral subluxation was found in 74.3% of the RSD group and 40% of the non‐RSD group (P = 0.004). In the non‐RSD group, 78.6% of the patients with subluxation and 38.1% of the patients without subluxation reported shoulder pain (P = 0.019). No correlation was found between the degree of shoulder pain and grade of subluxation in the non‐RSD group (P = 0.152). Conclude that the findings suggest that shoulder subluxation may be a causative factor for RSD. Therefore, prevention and appropriate treatment of glenohumeral joint subluxation should be included in rehabilitation of hemiplegic patients. Comment by Miles Day, MD. The purpose of this study was to examine the relationship between shoulder subluxation in hemiplegic patients and reflex sympathetic dystrophy. They also examined if subluxation is associated with shoulder pain and the grade of subluxation in patients with subluxation and no reflex sympathetic dystrophy (RSD). Patients with injuries to the rotator cuff of the brachial plexus, marked spasticity, and major trauma to joint structures were excluded as these can be precipitating factors for RSD. The study noted a significantly higher presence of shoulder subluxation within the RSD group and the presence of pain was significantly high in patients with shoulder subluxation in the non‐RSD group. The take home message of this article is that any measure or treatment that can be applied to the glenohumeral joint should be performed to eliminate the possibility of the patient developing RSD and subsequently hindering further rehabilitation in these patients.     

Evaluation of supraspinatus muscle changes in the shoulder joint of stroke patients with hemiplegic and shoulder subluxation using ultrasonography: comparison between affected and unaffected sides

[Purpose] The shoulder joint has a very unstable structure yet a significantly wide range of motion. Weakness of the muscles around the shoulder joint may cause shoulder joint subluxation. This study aimed to determine changes in supraspinatus muscle thickness between different shoulder abduction angles using ultrasonography and to compare differences in supraspinatus muscle thickness changes between the affected and unaffected sides depending on shoulder joint subluxation. [Participants and Methods] Forty hemiplegic patients with stroke were recruited (20 patients with and 20 without shoulder subluxation). Using ultrasonography, we measured supraspinatus muscle thickness at three shoulder joint abduction angles and calculated the differences in supraspinatus muscle thickness. Depending on subluxation, we separately analyzed the thickness and variations in the supraspinatus muscle on both the affected and unaffected sides. [Results] In stroke patients with shoulder subluxation, the difference in supraspinatus muscle thickness was significantly less in the affected side than in the unaffected side. [Conclusion] The thickness and rate of supraspinatus muscle thickness change was significantly less in the affected side than in the unaffected side in stroke patients with shoulder subluxation.     

Biomechanical analysis of four supports for the subluxed hemiparetic shoulder

External support systems, such as slings and lapboards, may reduce shoulder subluxation in individuals with hemiplegia. However there is controversy among occupational therapists concerning the most appropriate method to support the affected arm. The purpose of the present paper is to report the biomechanical analysis of four support systems; two shoulder support systems, a Bobath axillary roll, and a laptray. Two dimensional static biomechanical analyses determine the mechanical characteristics of each of these four support systems. The results of the analyses demonstrate the magnitude of the shoulder loading and the effectiveness of the various components of each of the systems. The effect of changing some of the characteristics of the slings is demonstrated. Slings with straps over the unaffected shoulder provide continuous support for the flaccid extremity. The Bobath axillary roll may introduce an unwanted lateral force. Lapboards must be maintained at an appropriate distance from the subluxed shoulder to be effective. This theoretical analysis of supports systems will provide therapists information to help them understand effective supports for subluxation.     

Arthrographic and clinical findings in patients with hemiplegic shoulder pain

OBJECTIVES: To identify the etiology of hemiplegic shoulder pain by arthrographic and clinical examinations and to determine the correlation between arthrographic measurements and clinical findings in patients with hemiplegic shoulder pain. DESIGN: Case series. SETTING: Medical center of a 1582-bed teaching institution in Taiwan. PARTICIPANTS: Thirty-two consecutive patients with hemiplegic shoulder pain within a 1-year period after first stroke were recruited. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Clinical examinations included Brunnstrom stage, muscle spasticity distribution, presence or absence of subluxation and shoulder-hand syndrome, and passive range of motion (PROM) of the shoulder joint. Arthrographic measurements included shoulder joint volume and capsular morphology. RESULTS: Most patients had onset of hemiplegic shoulder pain less than 2 months after stroke. Adhesive capsulitis was the main cause of shoulder pain, with 50% of patients having adhesive capsulitis, 44% having shoulder subluxation, 22% having rotator cuff tears, and 16% having shoulder-hand syndrome. Patients with adhesive capsulitis showed significant restriction of passive shoulder external rotation and abduction and a higher incidence of shoulder-hand syndrome (P=.017). Those with irregular capsular margins had significantly longer shoulder pain duration and more restricted passive shoulder flexion (P=.017) and abduction (P=.020). Patients with shoulder subluxation had significantly larger PROM (flexion, P=.007; external rotation, P<.001; abduction, P=.001; internal rotation, P=.027), lower muscle tone (P=.001), and lower Brunnstrom stages of the proximal upper extremity (P=.025) and of the distal upper extremity (P=.001). Muscle spasticity of the upper extremity was slightly negatively correlated with shoulder PROM. Shoulder joint volume was moderately positively correlated with shoulder PROM. CONCLUSIONS: After investigating the hemiplegic shoulder joint through clinical and arthrographic examinations, we found that the causes of hemiplegic shoulder pain are complicated. Adhesive capsulitis was the leading cause of shoulder pain, followed by shoulder subluxation. Greater PROM of the shoulder joint, associated with larger joint volume, decreased the occurrence of adhesive capsulitis. Proper physical therapy and cautious handling of stroke patients to preserve shoulder mobility and function during early rehabilitation are important for a good outcome.     

Glenohumeral malalignment in the hemiplegic shoulder. An early radiologic sign

A new radiologic sign is described which seems to diagnose an early presubluxation phase of glenohumeral malalignment in hemiplegic shoulders. The sign consists of a V-shaped widening of the upper part of the space between the humeral head and the glenoid cavity on anteroposterior shoulder films in the erect position. Twelve of 14 patients showing this sign went on to develop chronically painful shoulders, and four of them developed radiologically evident subluxation within several months. The sign may be helpful in diagnosing shoulder pathology following stroke at an early stage, when orthotic measures may still have preventive value.     

电刺激对肩关节半脱位及运动功能障碍的影响

目的探讨电刺激对肩关节半脱位及运动功能障碍的影响.方法中风并单侧肩关节半脱位患者59例,分为治疗组和对照组,治疗组患者应用二种方案的电刺激作用于肩关节周围肌肉,观察电刺激对肩关节半脱位、疼痛及运动功能障碍的影响.结果与对照组比较电刺激治疗能明显改善肩关节半脱位及运动功能障碍(P＜0.05).结论一定参数的电刺激可用于中风患者肩关节半脱位及运动功能障碍的治疗.     

Shoulder Pseudodislocation Associated with Calcific Tendinitis/Bursitis and Diagnosed by Point of Care Ultrasound

BackgroundShoulder pseudodislocation, or “drooping shoulder,” presents with acute pain and deformity of the joint, with radiographs demonstrating inferior subluxation of the humeral head relative to the glenoid fossa. The diagnosis must be made promptly and distinguished from true glenohumeral dislocation, both to avoid unnecessary attempts at closed reduction and to facilitate investigation of the underlying cause, which may include septic arthritis, hemarthrosis, or other emergent etiologies. Point-of-care ultrasound (POCUS) may be useful in the evaluation of emergency department (ED) patients with suspected pseudodislocation.Case ReportA 50-year old female presented to the ED with an acutely painful and deformed shoulder but atypical history and physical examination. Initial radiography appeared to show a glenohumeral dislocation, but POCUS, done to guide intra-articular lidocaine injection, led to recognition of pseudodislocation and subsequent diagnosis of calcific tendinitis/bursitis, a condition not previously associated with inferior humeral subluxation.Why Should an Emergency Physician Be Aware of This?Shoulder pseudodislocation must be considered in the evaluation of patients with suspected glenohumeral dislocation, but atypical features on history, physical examination, or initial plain radiography. POCUS may facilitate prompt diagnosis and identification of the underlying etiology.     

新型手臂吊带对脑卒中偏瘫患者肩关节半脱位的纠正作用及对转移能力的影响

目的观察新型手臂吊带对脑卒中偏瘫患者肩关节半脱位的纠正作用及对患者转移能力的影响。 方法共选取30例屈肘肌张力不高（改良Ashworth分级小于2级）并伴有肩关节半脱位的脑卒中偏瘫患者，分别在静态站立位下、10min坐站训练中及20min步行训练中采用3种方式（包括无任何承托及使用网袋式肩吊带或新型手臂吊带）处理偏瘫侧上肢，采用食指触诊法评估吊带对偏瘫患者肩关节半脱位的影响，并采用秒表测量上述2种吊带对患者5次坐站计时测试（FTSST）及站起走计时测试（TUG）结果的影响。 结果在静态站立位下，网袋式肩吊带及新型手臂吊带的治疗效果一致，均能有效纠正患者肩关节半脱位；经10min坐站训练后，发现新型手臂吊带对肩关节半脱位的纠正作用明显优于网袋式肩吊带（P<0.05），而网袋式肩吊带的纠正作用不显著（P>0.05），患者容易出现肩关节半脱位；经20min步行训练后，发现新型手臂吊带及网袋式肩吊带均能有效承托肩关节（P<0.05），并且以新型手臂吊带的纠正作用更显著（P<0.05）。与网袋式肩吊带比较，新型手臂吊带能有效减少坐站转移时间（P<0.05），而2种肩吊带对脑卒中偏瘫患者TUG计时结果均无显著影响（P>0.05）。 结论新型手臂吊带能有效纠正脑卒中偏瘫患者肩关节半脱位，同时对患者转移/移动能力提高可能具有积极作用。     

肘前臂托和传统肩吊带治疗脑卒中后肩关节半脱位的随机交叉研究

目的采用自身随机交叉对照研究方法, 分析和比较基于3D打印的肘前臂托(3D法)和传统肩吊带(传统法)对脑卒中后肩关节半脱位(GHS)的即时复位效果。方法选取8例符合入组条件的脑卒中后偏瘫伴GHS患者, 依次进行2个阶段的佩戴矫形器治疗, 每个阶段随机佩戴肘前臂托和传统肩吊带, 30 min/次, 2个阶段间隔24 h。所有患者检查6次肩关节X线正位片(分别是佩戴前健侧和患侧以及患侧2种矫形器每次佩戴即刻和佩戴30 min后), 分别测量肩峰下缘至肱骨头中心的垂直距离(VD)和水平距离(HD)。2次佩戴结束后, 对2种矫形器患者和家属进行满意度问卷调查。结果患者佩戴即刻和佩戴30 min后与同一方法佩戴前比较, VD和HD均有明显改善(P<0.05);但3D法的VD改善更加明显(P<0.01)。VD和HD在佩戴即刻和佩戴30 min后, 不同方法之间的差异均有统计学意义(P<0.05), 受试者对肘前臂托(3D法)的满意度更高。结论基于3D打印的肘前臂托和传统肩吊带对GHS都具有即时复位效果, 但肘前臂托复位效果更明显, 患者及其家属的使用满意度更高。     

Shoulder kinesthesia after anterior glenohumeral joint dislocation

The purpose of this study was to examine kinesthesia in normal (uninjured) shoulders and in shoulders with a history of glenohumeral joint dislocations. Both shoulders of 10 healthy subjects and 8 subjects with a history of unilateral anterior dislocation were tested for accuracy of angular reproduction, threshold to sensation of movement, and end-range reproduction using a motor-driven shoulder-wheel apparatus. An analysis of variance revealed significant differences (p less than .001) between the injured and uninjured shoulders for all three tests. Post hoc analysis showed significant differences (p less than .02) between the involved shoulders and all uninvolved shoulders. No significant difference was found among the uninvolved shoulders. The results of this study indicate that kinesthetic deficits occur after glenohumeral dislocation and may result in abnormal neuromuscular coordination and subsequent reinjury of the shoulder. Clinicians should consider rehabilitation of shoulder kinesthesia using therapeutic activation of the shoulder joint and muscle receptors when treating patients with previous dislocations.     

Comparing stimulation-induced pain during percutaneous (intramuscular) and transcutaneous neuromuscular electric stimulation for treating shoulder subluxation in hemiplegia

OBJECTIVE: To determine whether percutaneous (intramuscular) neuromuscular electric stimulation (perc-NMES) is less painful than transcutaneous neuromuscular electric stimulation (trans-NMES) for treating shoulder subluxation in hemiplegia. DESIGN: Double-blind, crossover trial. SETTING: University-affiliated tertiary care hospital. PARTICIPANTS: A convenience sample of 10 hemiplegic subjects with at least 1 fingerbreadth of glenohumeral subluxation. INTERVENTIONS: All subjects received 3 randomly ordered pairs of perc-NMES and trans-NMES to the supraspinatus and posterior deltoid muscles of the subluxated shoulder. Both types of stimulation were optimized to provide full joint reduction with minimal discomfort. MAIN OUTCOME MEASURES: Pain was assessed after each stimulation with a 10-cm visual analog scale (VAS) and the McGill Pain Questionnaire, using the Pain Rating Index (PRI) scoring method. Subjects were asked which type of stimulation they would prefer for 6 weeks of treatment. Wilcoxon's signed-rank test was used to compare median differences in VAS and PRI between perc-NMES and trans-NMES. RESULTS: Median VAS scores for perc-NMES and trans-NMES were 1 and 5.7, respectively (p = .007). Median PRI scores for perc-NMES and trans-NMES were 7 and 19.5, respectively (p = .018). Nine of the 10 subjects preferred perc-NMES to trans-NMES for treatment. CONCLUSION: Data suggest that perc-NMES is less painful than trans-NMES in the treatment of shoulder subluxation in hemiplegia.     

Biomechanical properties of the glenohumeral joint capsule in hemiplegic shoulder pain

Background

Although many hemiplegic shoulder patients have been suffering from limited range of motion, it is not fully established whether the pathologic biomechanics are same in hemiplegic shoulder pain and adhesive capsulitis. Therefore we aimed to investigate biomechanical properties of glenohumeral joint capsules of hemiplegic shoulder pain with limited range of motions.

Methods

Participants were 14 patients with hemiplegic shoulder pain, 10 controls, and 42 adhesive capsulitis patients matched with the hemiplegic shoulder pain group for sex, age, and range of motion. Demographic data, clinical variables, and sonographic findings were comparable between hemiplegic shoulder pain and adhesive capsulitis groups. We compared capsular capacity, maximal pressure, and capsular stiffness of glenohumeral joint capsule among the 3 groups.

Findings

Hemiplegic shoulder pain and adhesive capsulitis groups had smaller capsular capacity and higher maximal pressure than controls. The capsular stiffness of hemiplegic shoulder pain group was higher than that of controls (P = 0.001) but lower than that of adhesive capsulitis group (P < 0.001).

Interpretation

The stiffness of glenohumeral joint capsules in hemiplegic shoulder pain and adhesive capsulitis patients was substantially higher than that in controls, suggesting that hemiplegic shoulder pain patients had stiffer capsules as adhesive capsulitis patients did although the severities were different. This finding implicates that hemiplegic shoulder pain may share common pathologic properties of tighter capsules with adhesive capsulitis. However, there may be additional mechanisms contributing to range of motion limitation in hemiplegic shoulder pain because capsular stiffness in those patients was not as severe as that in adhesive capsulitis patients with similar range of motion limitation.     

早期综合性康复对偏瘫患者肩关节半脱位的影响

目的:探讨早期综合性康复治疗对偏瘫患者肩关节半脱位的疗效。方法 :对21例偏瘫患者肩关节半脱位进行早期综合性康复治疗 ,并与20例接受常规治疗的同病患者对照。结果 :4个月治疗后 ,两组间治愈率存在显著性差异(P<0.01)。结论 :早期综合性康复治疗对偏瘫患者肩关节半脱位有效。     

Shoulder pain and dysfunction in hemiplegia: effects of functional electrical stimulation

OBJECTIVE: To determine the influence of functional electrical stimulation (FES) on subluxation and shoulder pain in hemiplegic patients. DESIGN: Controlled study of 24 months' duration beginning in the first month after onset of stroke. SUBJECTS AND SETTING: One hundred twenty hemiplegic patients with both subluxed and painful shoulder were followed for rehabilitation before and after discharge between 1989 and 1993. All subjects received conventional rehabilitation based on the Bobath concept. In addition, patients were alternately assigned to a control group or to receive additional FES for 5 weeks on muscles surrounding their subluxed and painful shoulder. MAIN MEASURES: Clinical examinations, including range of motion, pain assessment, and x-rays, were performed at the start of the study, between the second and fourth weeks after onset of stroke, and subsequently at 6, 12, and 24 months. RESULTS: The FES group showed significantly more improvement than the control group in both pain relief (80.7% vs. 55.1%, p<.01) and reduction of subluxation (78.9% vs. 58.6%, p<.05). Furthermore, recovery of arm motion appeared to be significantly improved in the FES group (77.1% vs. 60.3% in the control group, p<.01). CONCLUSION: The FES program was significantly effective in reducing the severity of subluxation and pain and possibly may have facilitated recovery of the shoulder function in hemiplegic patients.     

体针结合本体感觉神经肌肉促进技术对急性期脑卒中偏瘫患者肩关节半脱位的疗效观察

目的研究体针与本体感觉神经肌肉促进技术相结合的疗法对急性期脑卒中偏瘫肩关节半脱位的疗效。方法选择急性期脑卒中偏瘫患者60例,随机分为本体感觉神经肌肉促进技术疗法组,体针结合本体感觉神经肌肉促进技术疗法组,各30例。对脑卒中偏瘫患者运动功能恢复及并发症的情况进行分析。结果体针结合本体感觉神经肌肉促进技术疗法对急性期脑卒中偏瘫患者肩关节半脱位的治疗,简化Fugl-Meyer上肢运动功能评分、肩肘关节活动度评估以及改良Barthel指数均明显优于单纯的本体感觉神经肌肉促进技术疗法,经t检验两组差异有显著性(P<0.05)。结论运用体针结合本体感觉神经肌肉促进疗法可有效加快急性期脑卒中偏瘫肩关节半脱位患者的治疗进程,改善日常生活活动能力,提高生活质量。     

Ultrasonographic measurement of shoulder subluxation in patients with post-stroke hemiplegia.

OBJECTIVE: To evaluate the ultrasonographic measurement of shoulder subluxation in patients with post-stroke hemiplegia. DESIGN: Prospective, single blind study. PATIENTS: A total of 41 patients with post-stroke hemiplegia were included (24 men and 17 women, mean age 56 years (standard deviation 11), age range 34-78 years). METHODS: Clinical evaluation of the affected shoulder was assessed using the Motricity Index scores and the Modified Ashworth Scale. Two ultrasonographic measurements were taken to check intra-rater reliability. The shoulder subluxation ratio was determined as the ratio of the radiographic vertical and horizontal distance, and the ultrasonographic lateral and anterior distances in the affected shoulder divided by that in the unaffected shoulder. RESULTS: Intraclass correlation coefficients of the repeated ultrasonographic lateral/anterior distance measurements in the unaffected and affected shoulders were 0.979/0.969 and 0.950/0.947, respectively. Ultrasonographic lateral/anterior distance ratios were negatively correlated with Motricity Index scores of the affected shoulder abduction (r = -0.490, p < 0.001/ r = -0.671, p < 0.001). Ultrasonographic anterior distance ratio was negatively correlated with Modified Ashworth Scale score of the affected shoulder (r = -0.374, p < 0.05). However, there was no correlation between radiographic distance ratios and clinical evaluation scores. CONCLUSION: We strongly recommend ultrasonography as a diagnostic tool to measure the degree of shoulder subluxation in patients with post-stroke hemiplegia.     

Comparative effectiveness of the GivMohr sling in subjects with flaccid upper limbs on subluxation through radiologic analysis

OBJECTIVE: To test the effectiveness of the GivMohr sling in reducing subluxation while providing joint compression through a flaccid limb, using the criterion standard of radiography for measuring subluxation. DESIGN: Anteroposterior 0 degree radiographs were taken of each subject: 1 of the unaffected shoulder and 3 of the affected shoulder; 1 without a sling, 1 with the GivMohr sling, and 1 with the Rolyan humeral cuff sling. SETTING: Two large rehabilitation centers. PARTICIPANTS: Twenty-five adult volunteers with a flaccid upper limb (UL) secondary to cerebrovascular accident or other pathology. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Vertical and horizontal subluxation were measured in millimeters on each of the 4 radiographs for each subject. RESULTS: A 1-way analysis of variance revealed a significant main effect for vertical but not horizontal subluxation. Post hoc tests showed that the GivMohr sling measures were similar to measures for the uninvolved shoulder, but significantly different from measures for the Rolyan and the involved shoulder. CONCLUSIONS: These results show that a properly fitted GivMohr sling reduces subluxation without overcorrecting. This new sling provides an alternative treatment option for persons with flaccid ULs that may prevent secondary complications and improve outcomes.     

In vitro quantitative assessment of total and bipolar shoulder arthroplasties: A biomechanical study using human cadaver shoulders

Background

Glenohumeral arthroplasty has produced results far inferior to those seen with hip and knee joint procedures. Therefore, the objective of this study was to evaluate the biomechanical parameters of the glenohumeral joint before and after total shoulder arthroplasty and bipolar hemiarthroplasty in 12 different positions simulating overhead activities.

Methods

Six matched pairs of cadaveric shoulders were used with a custom shoulder testing system to quantify the joint reactive force, contact areas, contact patterns and contact pressures in 12 different positions simulating overhead activities. The entire study was performed for the anatomic glenohumeral joint and following total shoulder arthroplasty on one side, and for the anatomic glenohumeral joint and following bipolar shoulder hemiarthroplasty on the contra-lateral side.

Findings

There was a significant increase in posterior force following total shoulder arthroplasty in two positions of horizontal adduction (P < 0.05). In positions of increased glenohumeral abduction and horizontal adduction, the contact pressures and patterns were greatly altered following both total shoulder arthroplasty and bipolar hemiarthroplasty procedures compared to the anatomic state.

Interpretation

The alterations in joint reaction force, contact pressure and contact patterns following shoulder arthroplasty suggest a possible etiology for glenoid component edge loading in patients following total shoulder arthroplasty. This edge loading may lead to a rocking phenomenon of the glenoid component and subsequent loosening.