Biomedical subjects

B F Morrey

Publications and source records attributed to B F Morrey.

At least 37 records · Page 2Linked to original sources

PubMed2001

Gait characteristics of patients with knee osteoarthritis.

The knee kinematics and kinetics of 139 patients (47 males and 92 females) with Grade II knee osteoarthritis (OA) were measured during level walking, stair ascent and stair descent. There was no significant difference in knee motion between the patients and normal subjects. The patients with knee OA had a significantly reduced internal knee extensor moment compared to normal subjects. This difference reflects the patient's compensation to reduce the knee joint loading. Further, subjects with OA and a higher body mass index have a lower knee extensor moment. The female subjects had significantly greater knee flexion and a greater knee extensor moment. This gender difference may partially explain the increased prevalence of OA in females. Most tests of OA treatments are assessed by criteria that do not reflect functional activities. This study demonstrates that objective gait analysis can be used to document gait adaptations used by patients with knee OA.

Adaptation, Physiological↗

PubMed2001

Retroperitoneal endometriosis causing unilateral hip pain.

BACKGROUND: The usual symptoms of endometriosis are secondary dysmenorrhea, dyspareunia, and infertility, but when located in the retroperitoneal space, it might have atypical symptoms that delay diagnosis and postpone therapy. CASE: A young nulligravida presented with secondary dysmenorrhea and concurrent cyclic hip pain. Recent laparoscopy was reportedly normal. Computed tomography (CT)-directed percutaneous needle biopsy of a retroperitoneal mass showed endometriosis. Laparotomy with retroperitoneal dissection removed the endometriosis, and operative arthroscopy released strictured hip tendons improving her hip pain and limp. CONCLUSION: Retroperitoneal endometriosis presenting as hip pain was diagnosed by CT-guided percutaneous needle biopsy permitting removal by a multidisciplinary surgical approach.

Adult↗

PubMed2001

Dynamic inferior stabilizers of the shoulder joint.

BACKGROUND: The glenohumeral joint is soft-tissue balanced. However, few studies have focused on its dynamic inferior stabilizers. OBJECTIVE: The objective of this study was to investigate the dynamic contributions of five shoulder muscles to inferior stability of the glenohumeral articulation in four joint positions. METHODS: The anterior, lateral and posterior deltoid, supraspinatus, short head of biceps, coracobrachialis and long head of triceps from ten cadaveric shoulders were tested in 0 degrees, 30 degrees, 60 degrees and 90 degrees of glenohumeral abduction. A constant inferior force of 15 N was applied to the humerus. The tendons were loaded sequentially in proportion to their respective muscle's cross-sectional area. Translations of the humeral head on the glenoid were recorded with a 3-Space tracking device. RESULTS: The lateral deltoid (8.2 mm, SD 4.8 mm) was potentially most effective in superior translation of the humeral head followed by the posterior deltoid (7.7 mm, SD 4.8 mm). The coracobrachialis and short head of biceps had considerable capability to translate the humeral head superiorly (2.8 mm, SD 1.3 mm) while the supraspinatus showed the weakest effects (1.3 mm, SD 0.5 mm). RELEVANCE: Strengthening exercises of the deltoid may be useful in the treatment of inferior glenohumeral instability, while the supraspinatus seems to be less important for inferior glenohumeral stability than previously assumed.

Biomechanical Phenomena↗

PubMed2001

The effect of forearm rotation on laxity and stability of the elbow.

OBJECTIVE: The purpose of this study was to quantify the relationship between forearm rotation and valgus/varus laxity of the elbow joint over the range of elbow flexion. BACKGROUND: There is little known about the influence of forearm rotation on the laxity and stability of the elbow joint. The general opinion exists that forearm rotation does not significantly influence the laxity and stability of the elbow joint. METHODS: Nine fresh-frozen cadaver elbows were used. Passive elbow flexion with the forearm in neutral rotation and in 40 degrees and 80 degrees of pronation and supination was performed under valgus/varus loads: (1) in intact elbows; (2) after a lateral surgical approach (lateral epicondylar osteotomy of the distal humerus); (3) after release of the anterior bundle of the medial collateral ligament; and (4) after release of the anterior bundle of the medial collateral ligament plus radial head resection. Valgus/varus elbow laxity was quantified using an electromagnetic tracking device. RESULTS: There was a statistically significant effect (P < 0.05) of forearm rotation on valgus/varus laxity throughout the range of flexion. The laxity was always greater in pronation than in supination, regardless of the surgical approach or the integrity of the anterior bundle of the medial collateral ligament or radial head. CONCLUSIONS: Valgus/varus laxity of the elbow is forearm rotation-dependent. The potential role of this effect should be considered and controlled for in the design of studies examining laxity and stability of the elbow joint. RELEVANCE: The observation that forearm pronation increases valgus/varus laxity, particularly in medial collateral ligament deficient elbows, implies a possible additional factor in throwing kinematics that might put professional baseball pitchers at risk of medial collateral ligament injury due to chronic valgus overload. Our data indicate that forearm rotation should be considered during the clinical examination of elbow instability.

Aged↗

PubMed2001

Dynamic contributions to superior shoulder stability.

It has been suggested that superior decentralization of the humeral head is a mechanical factor in the etiology of degenerative rotator cuff tears. This superior decentralization may be caused by muscular imbalance. The objective of this study was to investigate the contribution of individual shoulder muscles to superior stability of the glenohumeral joint. In 10 fresh frozen cadaver shoulders the tendons of the rotator cuff, teres major, latissimus, pectoralis major, deltoid and biceps were prepared. The shoulders were tested in a shoulder-loading device in 0 degrees, 30degrees, 60 degrees and 90 degrees of glenohumeral abduction. A constant superior force of 20 N was applied to the humerus. Tensile loads were applied sequentially to the tendons in proportion to their cross-sectional areas and translations of the humeral head relative to the glenoid were recorded with a 3Space Fastrak system. Depression of the humeral head was most effectively achieved by the latissimus (5.6 +/- 2.2 mm) and the teres major (5.1 +/- 2.0 mm). Further studies should elucidate their possible in vivo role in the frontal plane force couple to counter balance the deltoid. The infraspinatus (4.6 +/- 2.0 mm) and subscapularis (4.7 +/- 1.9 mm) showed similar effects while the supraspinatus (2.0 +/- 1.4 mm) was less effective in depression. Therefore, the infraspinatus and subscapularis should be surgically repaired whenever possible. The supraspinatus may be of less importance for superior stability than previously assumed.

Biomechanical Phenomena↗

PubMed2001

Complications of elbow arthroscopy.

BACKGROUND: Although the potential complications of elbow arthroscopy, including nerve injuries, have been described, the prevalence of their occurrence has not been well defined. The purpose of this paper is to describe the serious and minor complications in a large series of patients treated with elbow arthroscopy. METHODS: A retrospective review of 473 consecutive elbow arthroscopies performed in 449 patients over an eighteen-year period was conducted. Of the 473 cases, 414 were followed for more than six weeks. The most common final diagnoses were osteoarthritis (150 cases), loose bodies (112), and rheumatoid or inflammatory arthritis (seventy-five). The arthroscopic procedures included synovectomy (184), debridement of joint surfaces or adhesions (180), excision of osteophytes (164), diagnostic arthroscopy (154), loose-body removal (144), and capsular procedures such as capsular release, capsulotomy, and capsulectomy (seventy-three). RESULTS: A serious complication (a joint space infection) occurred after four (0.8%) of the arthroscopic procedures. Minor complications occurred after fifty (11%) of the arthroscopic procedures. These complications included prolonged drainage from or superficial infection at a portal site after thirty-three procedures, persistent minor contracture of 20 degrees or less after seven, and twelve transient nerve palsies (five ulnar palsies, four superficial radial palsies, one posterior interosseous palsy, one medial antebrachial cutaneous palsy, and one anterior interosseous palsy) in ten patients. The most significant risk factors for the development of a temporary nerve palsy were an underlying diagnosis of rheumatoid arthritis (p < 0.001) and a contracture (p < 0.05). There were no permanent neurovascular injuries, hematomas, or compartment syndromes in our series, and all of the minor complications, except for the minor contractures, resolved without sequelae. CONCLUSIONS: Our results indicate that the prevalence of temporary or minor complications following elbow arthroscopy may be greater than previously reported. However, serious or permanent complications were uncommon.

Adolescent↗

PubMed2001

Tardy posterolateral rotatory instability of the elbow due to cubitus varus.

BACKGROUND: Cubitus varus has long been considered merely a cosmetic deformity. The purpose of this paper is to demonstrate a causal relationship between cubitus varus and instability of the elbow. METHODS: In twenty-four patients (twenty-five limbs) with a cubitus varus deformity following a pediatric distal humeral fracture or resulting from a congenital anomaly (three limbs of two patients), tardy posterolateral rotatory instability of the elbow developed approximately two to three decades after the deformity occurred. All patients presented with lateral elbow pain and recurrent instability. The average varus deformity was 15 degrees (range, 0 degrees to 35 degrees ). Surgery was performed in twenty-one patients (twenty-two limbs). Treatment consisted of reconstruction of the lateral collateral ligament and osteotomy in seven limbs, ligament reconstruction alone in ten, osteotomy alone in four, and total elbow arthroplasty in one. RESULTS: In three patients, the triceps muscle was dynamically stimulated intraoperatively to contract while resisting extension of the elbow. This produced posterolateral rotatory subluxation of the elbow, which was reversed by corrective osteotomy and lateral transposition of a portion of the medial head of the triceps that originally had been attached to the elongated, deformed medial aspect of the olecranon. At an average of three years (minimum, one year) after the operation, the result was good or excellent for nineteen of the twenty-two limbs that had undergone an operation; three limbs had persistent instability. CONCLUSIONS: With cubitus varus, the mechanical axis, the olecranon, and the triceps line of pull are all displaced medially. The repetitive external rotation torque on the ulna permitted by these deformities can stretch the lateral collateral ligament complex and lead to posterolateral rotatory instability. Thus, cubitus varus deformity secondary to supracondylar malunion or congenital deformity of the distal part of the humerus may not always be a benign condition and may have important long-term clinical implications. Operative correction can relieve symptoms of instability. The indications for preventive corrective osteotomy remain to be determined.

Adolescent↗

PubMed2001

Poor outcomes of isolated tibial insert exchange and arthrolysis for the management of stiffness following total knee arthroplasty.

BACKGROUND: Severe stiffness after total knee arthroplasty is a debilitating problem. In patients with securely fixed and appropriately aligned components, arthrolysis of adhesions and exchange to a thinner tibial polyethylene insert may appear to be a reasonable and logical solution. We reviewed our experience with this procedure to determine its efficacy. METHODS: From 1992 through 1998, seven knees with marked stiffness after total knee arthroplasty were treated at our institution with arthrolysis of adhesions and conversion to a thinner tibial polyethylene insert. Only patients in whom the total knee prosthesis was well aligned, well fixed, and not associated with infection were included. There were five women and two men with a mean age at revision of sixty-one years (range, thirty-eight to seventy-four years). The average time to revision was twelve months, and the mean arc of motion prior to revision was 38.6 degrees (range, 15 degrees to 60 degrees ). The duration of follow-up after the insert exchange averaged 4.2 years (range, two to eight years). RESULTS: Mean Knee Society pain and function scores changed from 44 and 36.4 points preoperatively to 39.6 and 46 points at the time of final follow-up. Two knees were rerevised, one because of infection and the other because of aseptic loosening of the components. The five remaining knees were painful and stiff at the time of final follow-up. Four of these five knees were severely painful, and one knee was moderately and occasionally painful. The mean arc of motion of these five knees was 58 degrees (range, 40 degrees to 70 degrees ) at the time of final follow-up. CONCLUSION: Isolated tibial insert exchange, arthrolysis, and débridement failed to provide a viable solution to the difficult and poorly understood problem of knee stiffness in a group of carefully selected patients following total knee arthroplasty. We therefore have little enthusiasm for the continued use of this strategy.

Adult↗

PubMed2001

Retention of all-polyethylene acetabular components after femoral revision of a cemented total hip replacement.

BACKGROUND: This study was undertaken to provide a basis for decision-making when a well-fixed cemented cup is encountered at the time of a revision of a femoral component of a total hip replacement. It may be beneficial to retain the cup in some instances and thus reduce morbidity, complications, blood loss, operative time, and cost. METHODS: All patients who had a revision of the femoral component and retention of an all-polyethylene acetabular component from 1971 to 1996 were identified. Three hundred and seventy-four patients with a total of 395 cemented total hip replacements fit the inclusion criteria. The gender, date of and age at the index surgery, type of acetabular implant, and time of and reason for the revision of the femoral component were reviewed. The time to subsequent cup revision or latest surveillance was noted. The average age (and standard deviation) was 66.5 +/- 11.8 years at the time of the femoral revision, which was performed at an average of 8.0 +/- 4.4 years after the primary arthroplasty. For the purposes of this study, the end point for survival of the acetabular component was cup revision for any reason. RESULTS: At the time of the latest follow-up, at an average of nine years after the femoral revision and 17.3 years after the primary arthroplasty, 342 (86.6%) of the 395 cups remained in situ. Fifty-three cups (13.4%) in fifty-two patients had been revised, at an average of 10.0 +/- 5.7 years after the femoral revision and 16.7 +/- 5.3 years after the primary arthroplasty. The rate of survival of the retained acetabular components was 96.9% at five years, 89.3% at ten years, and 78.7% at fifteen years after the femoral revision and was 95.1% at fifteen years and 87.1% at twenty years after the primary arthroplasty. Increased age (p < 0.0001) and a shorter time-interval (less than 7.5 years) between the primary arthroplasty and the femoral revision (p = 0.05) were significantly associated with an increased likelihood of survival free of cup revision. Femoral head size, acetabular component design, gender, and primary diagnosis did not affect prosthetic survival in this sample of patients. CONCLUSIONS: The likelihood of survival of the unrevised cup was associated with patient age and duration of implantation, with the age of the patient being the more dominant factor predicting failure of the acetabular component.

Acetabulum↗

PubMed2001

Contribution of monoblock and bipolar radial head prostheses to valgus stability of the elbow.

BACKGROUND: The purpose of this study was to evaluate the stabilizing effect of radial head replacement in cadaver elbows with a deficient medial collateral ligament. METHODS: Passive elbow flexion with the forearm in neutral rotation and in 80 degrees of pronation and supination was performed under valgus and varus loads (1) in intact elbows, (2) after a surgical approach (lateral epicondylar osteotomy of the distal part of the humerus), (3) after release of the anterior bundle of the medial collateral ligament, (4) after release of the anterior bundle of the medial collateral ligament and resection of the radial head, and (5) after subsequent replacement of the radial head with each of three different types of radial head prostheses (a Wright monoblock titanium implant, a KPS bipolar Vitallium [cobalt-chromium]-polyethylene implant, and a Judet bipolar Vitallium-polyethylene-Vitallium implant) in the same cadaver elbow. Total valgus elbow laxity was quantified with use of an electromagnetic tracking device. RESULTS: The mean valgus laxity changed significantly (p < 0.001) as a factor of constraint alteration. The greatest laxity was observed after release of the medial collateral ligament together with resection of the radial head (11.1 degrees +/- 5.6 degrees). Less laxity was seen following release of the medial collateral ligament alone (6.8 degrees +/- 3.4 degrees), and the least laxity was seen in the intact state (3.4 degrees +/- 1.6 degrees). Forearm rotation had a significant effect (p = 0.003) on valgus laxity throughout the range of flexion. The laxity was always greater in pronation than it was in neutral rotation or in supination. The mean valgus laxity values for the elbows with a deficient medial collateral ligament and an implant were significantly greater than those for the medial collateral ligament-deficient elbows before radial head resection (p < 0.05). The implants all performed similarly except in neutral forearm rotation, in which the elbow laxity associated with the Judet implant was significantly greater than that associated with the other two implants. CONCLUSIONS AND CLINICAL RELEVANCE: This study showed that a bipolar radial head prosthesis can be as effective as a solid monoblock prosthesis in restoring valgus stability in a medial collateral ligament-deficient elbow. However, none of the prostheses functioned as well as the native radial head, suggesting that open reduction and internal fixation to restore radial head anatomy is preferable to replacement when possible.

Aged↗

PubMed2001

The unstable elbow.

Explore the source record for details and available documents.

Biomechanical Phenomena↗

PubMed2000

Ardeparin sodium for extended out-of-hospital prophylaxis against venous thromboembolism after total hip or knee replacement. A randomized, double-blind, placebo-controlled trial.

BACKGROUND: The optimal duration of prophylaxis against venous thromboembolism after total hip or knee replacement is uncertain. OBJECTIVE: To determine the efficacy and safety of extended out-of-hospital prophylaxis with low-molecular-weight heparin (ardeparin sodium). DESIGN: Randomized, double-blind, placebo-controlled trial. SETTING: 33 community, university, or university-affiliated hospitals. PATIENTS: 1195 adults who had elective total hip or knee replacement and completed 4 to 10 days of postoperative ardeparin prophylaxis. INTERVENTION: Daily subcutaneous ardeparin (100 anti-Xa IU/kg of body weight) or placebo from time of hospital discharge to 6 weeks after surgery. MEASUREMENTS: Symptomatic, objectively documented venous thromboembolism or death, along with major bleeding, from time of hospital discharge to 12 weeks after surgery. RESULTS: Patients who received ardeparin (n = 607) and those who received placebo (n = 588) did not differ significantly in the cumulative incidence of venous thromboembolism or death (9 cases [1.5%] compared with 12 cases [2.0%]; odds ratio, 0.7 [95% CI, 0.3 to 1.7]; P > 0.2; absolute difference, -0.56 percentage points [CI, -2.2 to 1.1 percentage points]) or major bleeding (2 cases [0.3%] compared with 3 cases [0.5%]). CONCLUSIONS: Among patients who had total knee or total hip replacement and received 4 to 10 days of postoperative ardeparin prophylaxis, the cumulative incidence of symptomatic venous thromboembolism or death after hospital discharge was not significantly reduced by extended out-of-hospital ardeparin prophylaxis. Extended ardeparin use could provide a maximum 2.2-percentage point true reduction in such events. The benefit of extended ardeparin use is not clinically important for most patients. Future research should identify high-risk patients who would benefit most from extended prophylaxis.

Adult↗

PubMed2000

Fractures of the distal humerus: role of elbow replacement.

Rigid osteosynthesis and early motion is the well-accepted norm to treat distal humerus fractures. This article addresses the role of elbow replacement related to fractures of the distal humerus, including indications, technique, and results. For severe posttraumatic osteoarthrosis, total elbow replacement using the semiconstrained Coonrad-Morrey prosthesis has proven to be a suitable and reliable option for older patients.

Adult↗

PubMed2000

The relevance of the moment arm of shoulder muscles with respect to axial rotation of the glenohumeral joint in four positions.

OBJECTIVE: This study was undertaken to determine the efficiency of the shoulder girdle muscles during axial humeral rotation based on measurements of the moment arms. DESIGN: The instantaneous muscle moment arms of 10 shoulder muscles, including the three portions of the deltoid, the rotator cuff muscles, teres major, and the thoracohumeral muscle group, were measured during four specified glenohumeral rotations. BACKGROUND: Axial humeral rotation is a commonly performed movement during activities of daily living and is a targeted motion of shoulder rehabilitation, particularly in those protocols emphasizing rotator cuff strengthening. An understanding of the function of the movers and stabilizers of the shoulder requires such basic information of muscle moment arms. METHODS: The instantaneous moment arm values of the muscles were derived from the slope of the plot of tendon excursion versus glenohumeral joint rotation angle. Motion studied included axial rotation with the humerus elevated 90 degrees in the coronal, scapular, and sagittal planes, as well as in the neutral position with the arm at the side. RESULTS: Based on the findings, with the humerus in both neutral and elevated positions, the infraspinatus is potentially the most powerful external rotator, followed by teres minor and posterior deltoid. Subscapularis and possibly pectoralis major are the most effective internal rotators in this position. CONCLUSIONS: The moment arm in providing axial humeral rotation of 10 shoulder muscles in four planes were obtained. In general, the teres minor and infraspinatus had the largest moment arms in external rotation, and the subscapularis had the largest moment arm in internal rotation. The muscle function for axial humeral rotation was found to be modified by the plane of arm elevation. RELEVANCE: The data could be used for developing exercise programs in physical therapy.

Adult↗

PubMed2000

Surgical treatment of extraarticular elbow contracture.

The problem of the contracted elbow is well-recognized for the circumstances under which it develops and the difficulty of operative and non-operative treatment. Earlier studies report this problem in an unfavorable manner; however, current studies suggest that posttraumatic stiffness of the elbow, particularly when the articular surface is left intact, may be treated reliably. The authors present a specific surgical approach to the elbow that has posttraumatic motion limitation described as extrinsic, that is, primarily attributable to contracture of the capsule and periarticular soft tissues. The limited surgical exposure termed the column procedure allows anterior capsular exposure through an interval in the brachioradialis and extensor carpi radialis longus. Using this procedure the authors report the treatment of 38 elbows (38 patients) with sufficient followup to accurately describe the postoperative course. At a mean of 3.5 years after surgery the total postoperative arc of motion improved from approximately 50 degrees to approximately 90 degrees. There were minimal complications. A static adjustable splint rather than physical therapy is used postoperatively. It is concluded that newer surgical techniques with carefully described programs can be successful in the majority of patients undergoing surgical release for extrinsic contracture of the elbow.

Contracture↗

PubMed2000

Treatment of the mobile, painful arthritic elbow by distraction interposition arthroplasty.

Between 1986 and 1994, 13 patients with mobile painful arthritic elbows were treated by distraction interposition arthroplasty using fascia lata. The mean period of follow-up was 63 months. An elbow distractor/fixator was applied for three to four weeks to separate the articular surfaces and to protect the fascial graft. Nine of the 13 patients (69%) had satisfactory relief from pain; eight (62%) had an excellent or good result by the objective criteria of the Mayo Elbow Performance score. Four have required revision to total elbow arthroplasty at a mean of 30 months with good results to date. Instability of the elbow, both before and after surgery, was found to be associated with unsatisfactory results. The rate of success when the procedure was performed for inflammatory arthritis was similar to that for post-traumatic arthritis, about 67%. Eight complications occurred in six patients, all in the group with post-traumatic arthritis. Two of these required further surgical procedures such as transposition of the ulnar nerve or repair of hernia of the fascia lata. Although less reliable than prosthetic replacement, distraction interposition arthroplasty is a useful option in the treatment of young, high-demand patients with arthritis of the elbow. It is rarely indicated in the presence of generalised inflammatory arthritis, but may be of value in those patients in whom the disease is limited primarily to the elbow.

Adult↗

PubMed2000

A conservative femoral replacement for total hip arthroplasty. A prospective study.

Between 1985 and 1993, 146 patients (162 hips) had total hip replacement (THR) using a conservative uncemented femoral component. The mean age of the patients was 50.8 years and the mean follow-up was 6.2 years (2 to 13). One patient was lost to follow-up, one died within two years of surgery and one had a revision procedure after a fracture sustained in a road-traffic accident. For the remaining 159, Kaplan-Meier survival analysis was calculated for the incidence of revision because of mechanical loosening or osteolysis. Survival without mechanical loosening at both five and ten years was 98.2%. Survival without osteolysis was 99% at five and 91% at ten years. The Harris hip score improved from a mean of 66.3 before to 90.4 at follow-up. Of particular note is the lack of thigh pain in this group. Radiological analysis showed that 139 stems (88%) had no measurable subsidence, 8 (5%) had less than 2 mm and 12 (7%) had more than 2 mm. Two of the eight and one of the 12 were revised for mechanical loosening. Nine hips were revised for late loosening associated with osteolysis. No reaming of the femoral canal was associated with statistically significant less blood loss compared with a comparable control group of uncemented implants (p < 0.0001). Our study suggests that using a conservative femoral implant does not protect against wear debris but the reliable mechanical stability (98.2%) makes this an attractive design of implant particularly for young patients.

Adult↗

PubMed2000

Dynamic glenohumeral stability provided by the rotator cuff muscles in the mid-range and end-range of motion. A study in cadavera.

BACKGROUND: Both static and dynamic factors are responsible for glenohumeral joint stability. We hypothesized that dynamic factors could potentially operate throughout the entire range of glenohumeral motion, although capsuloligamentous restraints (a static factor) have been thought to be primarily responsible for stability in the end-range of motion. The purpose of this study was to quantitatively compare the dynamic glenohumeral joint stability in the end-range of motion (the position of anterior instability) with that in the mid-range by investigating the force components generated by the rotator cuff muscles. METHODS: Ten fresh-frozen shoulders from human cadavera were obtained, and all soft tissues except the rotator cuff were removed. The glenohumeral capsule was resected after the rotator cuff muscles had been released from the scapula. A specially designed frame positioned the humerus in 60 degrees of abduction and 45 degrees of extension with respect to the scapula. The compressive and shear components on the glenoid were measured before and after a constant force was applied individually to each muscle with the humerus in five different positions (from neutral to 90 degrees of external rotation). The dynamic stability index, a new biomechanical parameter reflecting these force components and the concavity-compression mechanism, was calculated. The higher the dynamic stability index, the greater the dynamic glenohumeral stability. RESULTS: In the mid-range of motion, the supraspinatus and subscapularis provided higher dynamic stability indices than did the other muscles (p < 0.05). On the other hand, when the position of anterior instability was simulated in the end-range of motion, the subscapularis, infraspinatus, and teres minor provided significantly higher dynamic stability indices than did the supraspinatus (p < 0.005). CONCLUSIONS: The rotator cuff provided substantial anterior dynamic stability to the glenohumeral joint in the end-range of motion as well as in the mid-range. CLINICAL RELEVANCE: A glenohumeral joint with a lax capsule and ligaments might be stabilized dynamically in the end-range of motion if the glenoid concavity is maintained and the function of the external and internal rotators, which are efficient stabilizers in this position, is enhanced.

Aged↗