Posterior instability of the shoulder. A cadaver study

In a cadaver study of 15 shoulder specimens, the internal rotation of the joint was measured applying a constant internal torque of 1.5 Nm to the humerus. The specimens were suspended with the medial border of the scapula in vertical position. A lever fixed to the humerus was fitted with strain gauges for measurement of internal torque and sensors for measurement of internal rotation at different degrees of abduction from 0-90 degrees. Cutting the teres minor and infraspinatus muscle tendons increased internal rotation in the first 40 degrees of abduction. Internal rotation was further increased in this range by cutting also the proximal half of the posterior capsule. Lesion to the posterior capsular structures alone increased internal rotation from 40 degrees of abduction. In conclusion, among the posterior structures of the shoulder joint, the teres minor and the infraspinatus muscle tendons stabilize the joint for internal rotation in the first half of abduction, and the lower half of the capsule in the last part.     

Anterior and posterior shoulder instability: A cadaver study

In a cadaver study of 10 glenohumeral joint specimens, the anterior and posterior displacement of the humeral head was recorded after cutting parts of the rotator cuff and capsular structures applying a constant force to the humerus. The posterior structures were important for anterior stability in the first 40° of abduction. Anterior subluxation was changed to luxation in the first half of abduction, but only after lesions to the anterior part of the rotator cuff and upper half of the anterior capsule. For posterior displacement, the posterior part of the rotator cuff was found significant from 0-90° of abduction, and the posterior capsule between 40° and 90° of abduction. The anterior part of the rotator cuff and the upper part of the anterior capsule were essential in the first 40° of abduction. Cutting the capsular structures only, we found that the entire anterior capsule resisted anterior displacement for 70-90° of abduction, and the entire posterior capsule from 50-90° of abduction. For posterior displacement, the entire posterior capsule was important from 60 to 90° of abduction.

Clinically, a large lesion to the posterior structures seems to be essential for any major anterior displacement, and posterior displacement leading to subluxation only seems possible in connection with a major anterior injury.     

Anterior and posterior shoulder instability. A cadaver study

In a cadaver study of 10 glenohumeral joint specimens, the anterior and posterior displacement of the humeral head was recorded after cutting parts of the rotator cuff and capsular structures applying a constant force to the humerus. The posterior structures were important for anterior stability in the first 40 degrees of abduction. Anterior subluxation was changed to luxation in the first half of abduction, but only after lesions to the anterior part of the rotator cuff and upper half of the anterior capsule. For posterior displacement, the posterior part of the rotator cuff was found significant from 0-90 degrees of abduction, and the posterior capsule between 40 degrees and 90 degrees of abduction. The anterior part of the rotator cuff and the upper part of the anterior capsule were essential in the first 40 degrees of abduction. Cutting the capsular structures only, we found that the entire anterior capsule resisted anterior displacement for 70-90 degrees of abduction, and the entire posterior capsule from 50-90 degrees of abduction. For posterior displacement, the entire posterior capsule was important from 60 to 90 degrees of abduction. Clinically, a large lesion to the posterior structures seems to be essential for any major anterior displacement, and posterior displacement leading to subluxation only seems possible in connection with a major anterior injury.     

Posterior shoulder instability

The incidence, basic pathophysiology, and clinical and radiologic examination in posterior instability of the shoulder are discussed. Conservative treatment protocols and surgical procedures are presented.     

Posterior shoulder instability

Understanding the anatomic restraints to posterior shoulder instability and the resulting pathophysiology helps the treating physician make a correct diagnosis and formulate an appropriate treatment plan. A nonoperative program directed at reducing pain and increasing stability through comprehensive shoulder strengthening methods has generally been successful in treating recurrent posterior shoulder subluxation. Surgical options for treatment are reserved for those patients who fail to recognize improvement after six months of therapy and have no evidence of a psychological disturbance as the cause of their posterior instability.     

Posterior shoulder instability: approach to rehabilitation

The treatment of posterior shoulder instability can be a frustrating experience for both the patient and the clinician. Although operative versus nonoperative treatment of this problem has been debated in the literature, and various surgical approaches presented, little specific information can be found regarding the components of an effective rehabilitation program. This paper presents an overview of the dynamics of posterior shoulder subluxation and the authors ' approach to conservative management, with particular emphasis on therapeutic exercise techniques and procedures. J Orthop Sports Phys Ther 1989;10(12);488-494.     

Posterior shoulder pain and anterior instability: a preliminary clinical study

Different clinical tests have been suggested in the literature as significant indicators of anterior shoulder instability. Sometimes patients with recurrent anterior shoulder instability may show some muscular guarding thus making the evaluation of specific clinical tests very difficult. These patients may also report a medical history with posterior shoulder pain that can be also elicited during some clinical manoeuvres. From September 2005 to September 2006 we prospectively studied patients who underwent an arthroscopic anterior capsuloplasty. Shoulder clinical examination was performed including anterior shoulder instability tests (drawer, apprehension and relocation tests). Furthermore the exam was focused on the presence of scapular dyskinesia and posterior shoulder pain. The patients were also evaluated with ASES, Rowe, SST (Simple Shoulder Test), Constant and UCLA (University of California at Los Angeles) scoring system preoperatively and at the latest follow-up time. In the period of this study we observed 16 patients treated for anterior gleno-humeral arthroscopic stabilisation, who preoperatively complained also of a posterior scapular pain. The pain was referred at the level of lower trapezium and upper rhomboids tendon insertion on the medial border of the scapula. It was also reproducible upon local palpation by the examiner. Four of these patients also referred pain in the region of the insertion of the infraspinatus and teres minor. After arthroscopic stabilisation the shoulder was immobilised in a sling with the arm in the neutral rotation for a period of 4 weeks. A single physician supervised shoulder rehabilitation. After a mean time of 6.8 months of follow-up, all the shoulder scores were significantly improved and, moreover, at the same time the patients referred the disappearance of the posterior pain. Posterior scapular shoulder pain seems to be another complaint and sign that can be found in patients affected by anterior shoulder instability. It can also be related to eccentric work of posterior stabilising muscles of scapula during the altered biomechanics observed in case of anterior shoulder instability. This pain responds positively to surgical intervention showing that re-centring the humeral head probably also re-establishes the periscapular muscle-firing pattern with a mechanism mediated by the proprioceptive system.     

Posterior shoulder dislocation: Muscle and capsular lesions in cadaver experiments

In 10 cadaver shoulders, a posterior subspinous dislocation of the humeral head was provoked. All specimens showed total rupture of the posterior capsule and teres minor muscle, in most cases together with partial lesion in the infraspinatus muscle. In the majority of the specimens, lesions were also seen in the lower part of the subscapular muscle and in the proximal part of the anterior capsule.     

Posterior shoulder instability following anatomic total shoulder arthroplasty: A case report and review of management

We report a case of posterior shoulder instability following anatomic total shoulder arthroplasty (TSA). In addition, we present guidelines to aid in the management of posterior instability after TSA. A 50-year-old male underwent anatomic TSA for glenohumeral osteoarthritis. Postoperatively, the patient developed posterior instability secondary to glenoid retroversion. He did not improve despite conservative treatment. He underwent an arthroscopic posterior bone block procedure, 4-month after his index arthroplasty. At 14-month follow-up, the patient had regained near full motion and strength, and radiographs demonstrated osseous integration with no evidence of component loosening. Posterior instability following TSA is a relatively rare complication and challenging to manage. The posterior, arthroscopic iliac crest bone block grafting procedure represents a treatment option for posterior instability in the setting of a stable glenoid prosthesis following TSA.     

Subtalar instability: a biomechanical cadaver study

Hypothesis  

Subtalar instability is thought to be one of the possible causes for chronic functional instability of the foot and ankle. The purpose of this study was to determine the extent of ligament injury that is followed by subtalar instability and to depict consecutive pathologic joint motion.     

Posterior capsulolabral reconstruction in posterior shoulder instability: deltoid saving

To determine the efficacy of an open posterior capsulolabral reconstruction (PCLR) with a posterior deltoid-saving approach, 30 PCLRs in 29 patients with unidirectional posterior instability were reviewed retrospectively. The mean follow-up period was 30 months (range, 25-59 months). Posterior capsular redundancy was observed in all cases, but a posteroinferior labral tear was found in only 5. Posterior capsular thinning developed in 6 patients. According to the Rowe scale, 24 shoulders were rated as excellent, 1 as good, 2 as fair, and 3 as poor. The modified American Shoulder and Elbow Surgeons score at last follow-up was 91. During follow-up, recurrence of instability was observed in 4 cases, including 3 cases of voluntary instability. The overall recurrence rate was 13.3%, but the success rate was 92.6% when cases of voluntary instability were excluded. Whereas the midterm clinical results of PCLRs were satisfactory, the risk of recurrence was very high in patients with voluntary posterior instability, even though some subjective improvement could be obtained through a PCLR.     

Posterior shoulder instability: comprehensive analysis of open and arthroscopic approaches

Whether open surgery and arthroscopic repair of posterior shoulder instability have similar success rates remains unknown, but the literature suggests that arthroscopic soft-tissue stabilization procedures equal open surgery in managing posterior shoulder instability. A comprehensive PubMed computer search of the English-language literature from 1988 to 2004 was performed using the key phrase posterior shoulder instability. Studies included in our analysis addressed the surgical treatment of recurrent posterior instability and multidirectional instability with primarily a posterior component of instability; studies were excluded if their minimum follow-up was less than 1 year, if their patients had a history of habitual posterior shoulder instability, or if their patients had either bony procedures or thermal capsulorrhaphy. Data collected from each study included patient demographics, instability classifications (traumatic vs atraumatic), previous shoulder stabilizations, and clinical outcomes. After identifying and reviewing 283 abstracts, we found that 16 articles fulfilled the inclusion criteria--9 open studies (173 patients) and 7 arthroscopic trials (186 patients). The 2 treatment groups had similar sex distributions (P> .25). Mean age was 23 years for the open group and 26 years for the arthroscopic group (P< .02). Clinical outcomes were rated satisfactory by 72% of patients in the open group and 83% of patients in the arthroscopic group (P< .55), controlling for age. Eighty-five percent of patients treated with an open technique and 81% of patients treated arthroscopically returned to sports (P< .82). This study demonstrated no statistical difference in clinical outcomes for patients treated with either open or arthroscopic surgery for posterior shoulder instability.     

Prosthesis position in shoulder arthroplasty: A cadaver study of the humeral component

In six cadaver shoulder joints, the external rotation was measured applying a constant external torque to the humerus before and after insertion of a non-constrained shoulder joint prosthesis at different degrees of retroversion. At 35-45° of retroversion there was no difference between the external rotation of the inserted prosthesis and the external rotation of the joint before arthroplasty.     

Prosthesis position in shoulder arthroplasty: A cadaver study of the humeral component

In six cadaver shoulder joints, the external rotation was measured applying a constant external torque to the humerus before and after insertion of a non-constrained shoulder joint prosthesis at different degrees of retroversion. At 35-45° of retroversion there was no difference between the external rotation of the inserted prosthesis and the external rotation of the joint before arthroplasty.     

Posterior shoulder dislocation. Muscle and capsular lesions in cadaver experiments

In 10 cadaver shoulders, a posterior subspinous dislocation of the humeral head was provoked. All specimens showed total rupture of the posterior capsule and teres minor muscle, in most cases together with partial lesion in the infraspinatus muscle. In the majority of the specimens, lesions were also seen in the lower part of the subscapular muscle and in the proximal part of the anterior capsule.     

Anterolateral instability in the anterior cruciate ligament deficient knee: A cadaver study

Knee instability was evaluated in 13 normal osteoligamentous knee preparations after transection of the anterior cruciate ligament. Abduction-adduction rotation, coupled tibial translatory movement, and coupled tibial axial rotation were recorded continuously and simultaneously during flexion or extension while applying a well defined valgus directed moment and during extension while applying an anterior tibial force. As a result of the valgus-directed moment, an increase was found in abduction rotation, in coupled anterior tibial translation, and in coupled internal tibial axial rotation. Coupled rotatory and translatory instabilities were larger, and maximum instability was observed at a smaller knee angle during the extension movement than during the flexion movement. The pattern of the instability, excited as a result of the valgus moment, was different from the instability excited as a result of an anterior tibial force.