Bilateral non-traumatic hip fractures in a heavy smoker COPD patient on inhaled steroids.

INTRODUCTION: Bilateral proximal femoral fractures without trauma are very rare conditions. They have been reported in connection with osteoporosis, renal osteodystrophy, parathyroid disease, tumors, epileptic seizures, electroconvulsive therapy, and postirradiation. METHOD: We present a case of a 75-year-old man with bilateral hip fractures. No trauma, neurological, endocrinological disorder, or malignancy was reported in his history. He had a background of chronic obstructive pulmonary disease (COPD) and had been taking inhaled steroids (budesonide) 800 µg per day for 10 years. He was a heavy smoker with a smoking history of 120 packs/year. His complaints had initially started as pain on the left hip and groin and then had progressed to the right in 10 days. Plain x-rays of the pelvis showed left femoral neck and right subtrochanteric femoral fractures. Fixation with proximal femoral nail of the right hip and partial arthroplasty of the left hip was performed on the following day after his admission. Pathological examination revealed osteoporosis in bone samples from both hips. RESULT: COPD and osteoporosis have some common risk factors. Smoking, decreased exercise capacity, inhaled, or oral steroid therapy may increase osteoporosis and risk of bone fractures by decreasing bone mineral density. Non-traumatic femoral fractures may occur in patients on long-term inhaled steroid treatment for chronic airway diseases such as asthma and COPD. CONCLUSION: History of COPD with corticosteroid use may be used as a diagnostic tool to identify patients having osteoporosis. Preventive measures can be performed by monitoring high-risk patients with bone mineral densitometry, WHO fracture risk assessment tool (FRAX tool), serum calcium, and vitamin D levels to prevent bone fractures. Treating those patients with the lowest effective dose of corticosteroids should be targeted.

Short-term results of surgical treatment with cephalomedullary nails for basicervical proximal femoral fractures.

The treatment of basicervical femoral fractures remains controversial. The aim of this study was to examine the efficacy of intramedullary nail use in the surgical treatment of basicervical fractures. In total, 28 patients with basicervical fractures treated with proximal femoral nails were examined retrospectively. Fracture healing was observed in all patients, who were followed at least for 6 months. While the average radiological fracture healing timing was ~10.5 (8-14) weeks, clinical fracture healing occurred in 6 (5-9) weeks on average. Screw cut­out, avascular necrosis, femur fracture, and surgical wound infections did not occur in any patient. Severe collapse (>10%) was not noted in any patient. The postoperative mean Harris hip score was 81.2±21.3. Osteosynthesis application with a proximal femoral nail in basicervical proximal femur fractures is a surgical treatment that can be performed with minimally invasive techniques without open surgery. This is a rapid, sound, and simple treatment method with low morbidity.

Bilateral, locked, recurrent anterior shoulder dislocation: case report.

Bilateral anterior dislocation of the shoulder is a rare condition. Most of the cases are seen as posterior dislocations which generally occur during diffuse tonic-clonic contractions of epileptic seizures or after being exposed to strong electric shock. In this article, we report a 21-year-old epileptic patient who had severe bilateral shoulder pain and joint restriction. Diagnoses of bilateral, locked, anterior shoulder dislocation and Hill-Sachs lesions were made with shoulder X-rays and computed tomography. Arthroscopic Bankart repair and remplissage technique were applied in surgical treatment of both shoulders. Posterior dislocations of shoulder usually occur during epileptic seizures but anterior dislocations are rare in the literature. This may lead to delay in diagnosis. Computed tomography scan may be helpful in making diagnosis in uncertain patients. It should not be forgotten that recurrent anterior dislocations may be seen in epileptic patients. Such dislocations should be followed up regularly and instability must be treated to prevent excessive damage to the shoulder.

Sagittal spinopelvic parameters in children with achondroplasia: identification of 2 distinct groups.

OBJECT: Spinopelvic parameters in children with achondroplasia have not been described. Because they observed a unique sagittal spinopelvic phenotype in some achondroplastic children with very horizontal sacrums, the authors sought to quantify the spinopelvic parameters in a pediatric patient population. METHODS: A retrospective review was performed to identify all children (age range 1 month-10 years) with a diagnosis of achondroplasia between 2004 and 2009. Clinical and radiographic data were analyzed for age, sex, lumbar lordosis (LL), thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), sacral slope (SS), pelvic tilt (PT), and pelvic incidence (PI). Differences among these variables were analyzed using a 2-tailed, unpaired Student t-test. RESULTS: Forty children, 23 males and 17 females, with achondroplasia were identified during the study period. The mean age was 2.6 years. Two groups of patients were identified based on PT (that is, negative or positive tilt and horizontal or not horizontal sacrum). A negative PT was identified in all children with an extremely horizontal sacrum. Seventeen children had a negative PT (mean -16.6°), and the mean parameters in this group were 65.4° for LL, 31.7° for TLK, 18.5° for TK, 43.3° for SS, and 26.4° for PI. Twenty-three children had a positive PT (mean 17.9°), and the mean parameters in this group were 53.4° for LL, 41.5° for TLK, 9.6° for TK, 30.8° for SS, and 43.8° for PI. A statistically significant difference was observed for LL (p = 0.01), TLK (p = 0.05), SS (p = 0.006), PT (p = 0.006), and PI (0.0002). CONCLUSIONS: Spinopelvic parameters in achondroplasia are potentially dichotomous. The future implications of this observation are not known and will need to be explored in future long-term studies that follow pediatric patients with achondroplasia through adulthood.

Treatment of chronic lateral instability of the ankle with the Colville technique: a prospective analysis with minimum five years of follow-up.

OBJECTIVES: This study aims to prospectively analyze of the long-term results of the Colville's technique for the treatment of chronic lateral ankle instabilities. PATIENTS AND METHODS: Twenty-eight ankles of 28 male patients (mean age 24.6 years; range 20 to 35 years) which were treated using Colville's technique were evaluated with a mean follow-up of 76.1 months (range 60 to 106 months). Ankle instability, ankle functions and outcomes in the last visit were assessed and statistically compared. Stress radiographs with the TELOS device were repeated at six-months and five-years after surgery and compared with the stability of the uninjured ankle. RESULTS: Twenty-three of the results were excellent and five were good according to the criteria of Chrisman and Snook. All patients returned to normal daily activity levels at an average of eight months following surgery. Radiographic analysis revealed the significant preservation of stability at least five years after surgery with no sign of arthritis. The difference between preoperative and sixth-months postoperative values of both the talar tilt and the anterior draw tests were found statistically significant, indicating significant correction of the laxity. On contrary, difference between sixth months and five year values were not statistically significant, indicating the preservation of the correction. CONCLUSION: Anatomical augmented reconstruction procedure of Colville's is a long-lasting and good alternative compared to other more complex techniques of reconstruction with minimum long-term complications.

Bilateral traumatic dislocation without fracture of the lumbosacral junction: case report and review of the literature.

STUDY DESIGN: Case report. OBJECTIVE: The diagnosis and surgical management of a patient with a traumatic bilateral dislocation of the lumbosacral junction (L5-S1) without facet or pars interarticularis fracture is presented with a thorough review of the existing literature. SUMMARY OF BACKGROUND DATA: Lumbar fracture-dislocations have been widely reported. However, only five cases of lumbosacral junction dislocation without a fracture have been previously reported. METHODS: A 23-year-old patient was involved in a high-energy occupational injury and presented with complaints of back pain and inability to ambulate. Neurological assessment confirmed adequate motor strength (4+/5 bilaterally), normal perianal and lower extremity sensation, and urinary retention (postvoid residual: 1000 mL). Imaging studies revealed bilateral L5-S1 facet dislocation (bilateral jumped facets) without articulating processes or pars interarticularis fractures. Three-column ligamentous injury was confirmed on magnetic resonance imaging with complete tear of the ligamentum flavum, anterior and posterior longitudinal ligaments, interspinous and supraspinous ligaments, and avulsion of the L5 spinous process. The patient underwent bilateral facetectomies, diskectomy, laminectomies, and reduction of slippage with interbody and posterolateral transpedicular instrumented fusion. RESULTS: At 1-year follow-up, the patient reported mild back pain well controlled with naproxen. He continued to report good improvement in his daily function. CONCLUSION: A careful clinical examination and imaging assessment must be done for appropriate diagnosis and treatment of this rare type of injury. Reduction in the face of intact articulating processes and pars interarticularis is challenging because of acting heavy forces on the lumbosacral joint. Facetectomies, nerve root decompression, and circumferential instrumented fusion are ways to decompress the neural elements, restore alignment, and maintain segmental stability.

Hemorrhagic synovial cyst: the possible role of initial trauma and subsequent microtrauma in its pathogenesis: case report.

BACKGROUND AND IMPORTANCE: Intraspinal synovial cysts are uncommon causes of back and radicular leg pain. Usually associated with degenerative spinal disease, these juxtafacet cysts are usually located in the lumbar spine and may rarely undergo intracystic hemorrhage. The pathogenesis of these cysts are unclear, and risk factors that may contribute to hemorrhagic complications are largely unknown. CLINICAL PRESENTATION: A 68-year-old man presented to the clinic 4 months after a fall on ice with persistent back pain and lumbar radiculopathy. A week after the initial clinic consultation, the patient presented to the emergency room with increased pain and worsening weakness in the left foot. An emergent magnetic resonance image showed thecal sac compression secondary to a large, juxtafacet cyst that was hyperintense on T1-weighted and hypointense on T2-weighted images. Lumbar decompressive laminectomies were performed at L3 and L4 with cyst removal and stabilization. CONCLUSION: We present the eighth reported case of a hemorrhagic juxtafacet cyst secondary to physical trauma, the second in which the patient's symptoms acutely worsened several months after the initial insult without new trauma. We also present summary statistics of the 31 cases of hemorrhagic juxtafacet cysts reported in the literature and propose a putative mechanism that may account for the development and progression of symptoms in some patients.

Sacral tumor resection and the impact on pelvic incidence.

OBJECT: pelvic incidence (PI) directly regulates lumbar lordosis and is a key determinant of sagittal spinal balance in normal and diseased states. Pelvic incidence is defined as the angle between the line perpendicular to the S-1 endplate at its midpoint and the line connecting this point to a line bisecting the center of the femoral heads. It reflects an anatomical value that increases with growth during childhood but remains constant in adulthood. It is not altered by changes in patient position or after traditional lumbosacral spinal surgery. There are only 2 reports of PI being altered in adults, both in cases of sacral fractures resulting in lumbopelvic dissociation and sacroiliac (SI) joint instability. En bloc sacral amputation and sacrectomy are surgical techniques used for resection of certain bony malignancies of the sacrum. High, mid, and low sacral amputations result in preservation of some or the entire SI joint. Total sacrectomy results in complete disruption of the SI joint. The purpose of this study was to determine if PI is altered as a result of total or subtotal sacral resection. METHODS: the authors reviewed a series of 42 consecutive patients treated at The Johns Hopkins Hospital between 2004 and 2009 for sacral tumors with en bloc resection. The authors evaluated immediate pre- and postoperative images for modified pelvic incidence (mPI) using the L-5 inferior endplate, as the patients undergoing a total sacrectomy are missing the S-1 endplate postoperatively. The authors compared the results of total versus subtotal sacrectomies. RESULTS: twenty-two patients had appropriate images to measure pre- and postoperative mPI; 17 patients had high, mid, or low sacral amputations with sparing of some or the entire SI joint, and 5 patients underwent a total sacrectomy, with complete SI disarticulation. The mean change in mPI was statistically different (p < 0.001) for patients undergoing subtotal versus those undergoing total sacrectomy (1.6° ± 0.9° vs 13.6° ± 4.9° [± SD]). There was no difference between patients who underwent a high sacral amputation (partial SI resection, mean 1.6°) and mid or low sacral amputation (SI completely intact, mean 1.6°). CONCLUSIONS: the PI is altered during total sacrectomy due to complete disarticulation of the SI joint and discontinuity of the spine and pelvis, but it is not changed if any of the joint is preserved. Changes in PI influence spinopelvic balance and may have postoperative clinical importance. Thus, the authors encourage attention to spinopelvic alignment during lumbopelvic reconstruction and fixation after tumor resection. Long-term studies are needed to evaluate the impact of the change in PI on sagittal balance, pain, and ambulation after total sacrectomy.

Fibrin sealant in the treatment of acute ruptures of the Achilles tendon: long-term results.

OBJECTIVES: This study aims to point out the long-term results of fibrin sealant in the treatment of acute ruptures of the Achilles tendon. PATIENTS AND METHODS: Between January 1998 and December 2007, 42 patients (42 males; mean age 37.8 years; range 27 to 56 years) admitted to our clinic for acute ruptures of the Achilles tendon were treated with a fibrin sealant. The average time to surgery from injury was 2.0 (range 1 to 4) days. The patients were divided into two groups; in the first 32 patients fibrin sealant was used which was heated for preparation. In the second group of 10 patients we used fibrin sealant which did not require heating for preparation. RESULTS: The mean follow-up period was 51.5 (range 24 to 92) months. The Thermann scoring system was used to evaluate the patients postoperatively in both the early and the final follow-ups. We found that the Thermann scores of some patients slightly decreased in the advanced age group when compared to younger patients long-term, but the overall result remained unchanged by time. Only one patient needed to be re-operated for a re-rupture resulting from resumption of daily work and sports activities. CONCLUSION: Treatment of acute Achilles tendon ruptures with fibrin sealant can be one of the first choices selected because of its lower complication rate and equal results when compared to other treatment options.

Pediatric tethered cord syndrome: response of scoliosis to untethering procedures. Clinical article.

OBJECT: Tethered cord syndrome (TCS) is frequently associated with scoliosis in the pediatric population. Following spinal cord untethering, many patients continue to experience progression of spinal deformity. However, the incidence rate, time course, and risk factors for scoliosis progression following tethered cord release remain unclear. The aim of this study was to determine factors associated with scoliosis progression and whether tethered cord release alone would halt curve progression in pediatric TCS. METHODS: The authors retrospectively reviewed 27 consecutive pediatric cases of spinal cord untethering associated with scoliosis. The incidence rate and factors associated with scoliosis progression (> 10 degrees increased Cobb angle) after untethering were evaluated using the Kaplan-Meier method. RESULTS: The mean age of the patients was 8.9 years. All patients underwent cord untethering for lower-extremity weakness, back and leg pain, or bowel and bladder changes. Mean +/- SD of the Cobb angle at presentation was 41 +/- 16 degrees . The cause of the spinal cord tethering included previous myelomeningocele repair in 14 patients (52%), fatty filum in 5 (18.5%), lipomeningocele in 3 (11%), diastematomyelia in 2 (7.4%), arthrogryposis in 1 (3.7%), imperforate anus with an S-2 hemivertebra in 1 (3.7%), and lipomyelomeningocele with occult dysraphism in 1 (3.7%). Mean follow-up was 6 +/- 2 years. Twelve patients (44%) experienced scoliosis progression occurring a median of 2.4 years postoperatively and 8 (30%) required subsequent fusion for progression. At the time of untethering, scoliosis < 40 degrees was associated with a 32% incidence of progression, whereas scoliosis > 40 degrees was associated with a 75% incidence of progression (p < 0.01). Patients with Risser Grades 0-2 were also more likely to experience scoliosis progression compared with Risser Grades 3-5 (p < 0.05). Whereas nearly all patients with Risser Grades 0-2 with curves > 40 degrees showed scoliosis progression (83%), 54% of patients with Risser Grades 0-2 with curves < 40 degrees progressed, and no patients with Risser Grades 3-5 with curves < 40 degrees progressed following spinal cord untethering. CONCLUSIONS: In this experience with pediatric TCS-associated scoliosis, patients with Risser Grades 3-5 and Cobb angles < 40 degrees did not experience curve progression after tethered cord release. Patients with Risser Grades 0-2 and Cobb angles > 40 degrees were at greatest risk of curve progression after cord untethering. Pediatric patients with TCS-associated scoliosis should be monitored closely for curve progression using standing radiographs after spinal cord untethering, particularly those with curves > 40 degrees or who have Risser Grades 0-2.

Incidence of symptomatic retethering after surgical management of pediatric tethered cord syndrome with or without duraplasty.

BACKGROUND: Cord retethering and other postoperative complications can occur after the surgical untethering of a first-time symptomatic tethered cord. It is unclear if using duraplasty vs. primary dural closure in the initial operation is associated with decreased incidence of either immediate postoperative complications or subsequent symptomatic retethering. It is also unclear if different etiologies are associated with different outcomes after each method of closure. We reviewed our pediatric experience in first-time surgical untethering of symptomatic tethered cord syndrome (TCS) to identify the incidence of postoperative complications and symptomatic retethering after duraplasty vs. primary closure. MATERIALS AND METHODS: We retrospectively reviewed 110 consecutive pediatric (<18 years old) cases of first-time symptomatic spinal cord untethering at our institution over a 10-year period. Incidence of postoperative complications and symptomatic retethering were compared in cases with duraplasty vs. primary dural closure use. RESULTS: Mean age was 5.7 +/- 4.8 years old. "Complex" etiologies included lipomyelomeningocele or prior lipomyelomeningocele repair in 22 (20%) patients, prior myelomeningocele repair in 35 (32%), and concurrent lumbosacral lipoma in 18 (16%). "Noncomplex etiologies" included fatty filum in 26 (24%) and split cord malformation in five (4%). Seventy-five (68%) cases underwent primary dural closure vs. 35 (32%) with duraplasty. Twenty-nine (26%) patients experienced symptomatic retethering at a median [interquartile range (IQR)] of 30.5 [20.75-41.75] months postoperatively. There was no difference in incidence of postoperative cerebrospinal fluid leak, surgical site infection, or median [IQR] length of stay in patients receiving primary dural closure [4 (5%), 7 (9%), and 5 (4-6) days, respectively] vs. duraplasty [3 (9%), 3 (9%), and 6 [5-8] days, respectively], p > 0.05. Complex etiologies were more likely to retether than noncomplex etiologies after primary closure (33.6% vs. 6.6%, p = 0.05) but not after duraplasty (13.7% vs. 5.4%, p = 0.33). Duraplasty graft type (polytetrafluoroethylene vs. bovine pericardium) was not associated with pseudomeningocele or retethering. CONCLUSION: In our experience, the increased rate of symptomatic retethering observed with complex pediatric TCS (pTCS) etiologies after primary dural closures was not observed when duraplasty was instituted. Expansile duraplasty may be valuable specifically in the management of patient subgroups with complex pTCS etiologies.

Comparison of outcomes of two different surgeries in regarding to complications for chronic anterior shoulder instability.

INTRODUCTION: The purpose of this study is to compare the early clinical results of two techniques in regarding to complications in the patients who suffered from chronic anterior traumatic isolated shoulder instability. METHOD: Eighty-five patients underwent reconstructive procedures due to chronic isolated traumatic shoulder instability in our clinic between 1990 and 2002. Sixty-four patients in whom preoperatively Bankart lesion were detected with MRI and who participated in the regular follow-up were included in the study. Thirty-four patients were treated with Bankart repair (Group I) and 30 patients were treated with Modified Bristow procedure (Group II). Mean follow-up period was 25 (24-39) months for group I and 28 (24-96) months for group II. All cases were evaluated preoperatively and postoperatively according to Rowe scoring system. RESULTS: Mean Rowe scores were 90 and 88.1 for group I and II, respectively. Due to recurrent dislocation, four revision surgeries (one in group I, three in group II) were performed. Surgical complications were encountered in group II, just as fracture at the bone block in four cases, nonunion in five cases and removal of loose screw in one case. DISCUSSION: According to clinical outcomes, both the techniques are useful and feasible for the treatment of the chronic traumatic isolated anterior shoulder instability; however, complication rate is higher in the Modified Bristow technique and, Bankart repair is directed to the anatomic repair of the original pathology.

Treatment of rupture of the Achilles tendon with fibrin sealant.

BACKGROUND: The optimal management strategy for acute Achilles tendon ruptures is controversial. These injuries historically were treated by nonoperative methods (cast immobilization, bandaging); however, operative repair of the ruptured tendon has become popular. METHODS: Thirty-two patients who had rupture of the Achilles tendon were treated operatively with use of fibrin sealant, and clinical and functional performance measures were assessed after a mean followup of at least 6 months between November, 1998, and July, 2003. All of the patients were male. Average age was 38.18 (30 to 45) years. All of the patients were followed for at least 18 months after surgery. Average followup time was 22.4 (18 to 56) months. We evaluated all patients according to the scoring system of Thermann et al. RESULTS: Our results were excellent in 24 patients and good in eight patients. One patient had rerupture 3 weeks after surgery. CONCLUSION: Fibrin sealants are biologically compatible, hemostatic agents derived from human plasma that can be used instead of suture or suture support. We think that the treatment of rupture of the Achilles tendon with fibrin sealant is a useful treatment, and there is less risk of complications, such as deep infection, than in other operative procedures. We had no wound closure problems, the incision size was small, and the operating time was short. However, it must be remembered that the risk of disease transfer by fibrin sealant application is still present.

Effects of time lapse on results of partial nerve injury repair.

Partial nerve severance is a problem in peripheral-nerve surgery. It should be repaired without tension for a good functional result. There is usually no trouble in repairing acute injuries. But, as time passes, it may be difficult to establish a proper end-to-end repair, and this cause more tension at the repair sites. In this study, the critical time lapse for a deleterious effect was evaluated. Thirty rats were used, with partial nerve severance repaired immediately or at 10 or 20 days later. At 2, 4, 8, 12, 20, and 28 weeks, functional assessment of nerve regeneration was performed using walking-track analysis. Functionally, the sciatic index values were very close to each other in the immediate and 10-day-delay group, but the difference between these groups and the 20-day-delay group was statistically significant. The study suggests a critical period of about 2 weeks after partial nerve section before irreversible changes occur. Although this is not applicable to human models, it implies further work on a primate model for determining a reliable time-lapse period.

Late reconstruction of neglected metacarpal shaft defects due to gunshot wound.

We evaluated eight patients after delayed treatment of nine metacarpal bone defects due to gunshot injuries. The mean length of the metacarpal defects was 3 cm and the average time between the gunshot injury and the reconstruction surgery was 10 months. Although all of the patients had been treated with wound irrigation and debridement immediately following injury, no attempt had been made to repair the metacarpal defect or to maintain metacarpal length. As a result, serious shortening had occurred. After the original length of the metacarpal had been restored by distraction of the soft tissues (1 mm/day), a tri-cortical iliac bone graft was inserted into the bone defect. The average follow-up time was 15 months. Clinical and radiological union was established in all cases after an average of 12 weeks. The mean grip strength of the hand and the mean range of motion of the metacarpophalangeal joint increased by 24% and 60%, respectively.

Biodegradable implants in the treatment of scaphoid nonunions.

We reviewed 12 male patients with scaphoid nonunions treated by open reduction, bone grafting, and internal fixation with biodegradable implants made of self-reinforced poly- l-lactic acid. Mean patient age was 22.5 (20-25) years. Ten patients had type D2 scaphoid nonunions with a fracture line in the middle one third, one patient had type D2 nonunion with a fracture line in the proximal one third, and one patient had type D1 distal one-third fibrous union. The mean wrist score (modified Mayo wrist score) was 20.8 (10-40) preoperatively and improved after 22-80 months (55-90). All nonunions healed, and the mean solid union time was 4.5 (3.5-7) months. We obtained excellent results in five patients, good results in four, fair results in two, and a poor result in one. The results of this study offer a valid alternative in the fixation of scaphoid nonunions. The major advantage of biodegradable materials is to eliminate the requirement for the removal of the fixation material.

Proximal oblique crescentic osteotomy in hallux valgus.

Twenty-six patients with moderate-to-severe hallux valgus deformities were evaluated before and after treatment. All of the patients had incongruent great toe joints. The patients underwent modified proximal crescentic osteotomy, which was termed proximal oblique crescentic osteotomy. The results were evaluated at an average follow-up time of 55 weeks. Objective criteria were hallux valgus angle, intermetatarsal angle, shortening of the first metatarsal, and angulation at the osteotomy site. Clinical evaluation was made according to the rating system of the American Orthopaedic Foot and Ankle Society. The mean correction of the hallux valgus and intermetatarsal angles was 22.1 degrees and 9.9 degrees, respectively. Short-term results indicate that proximal oblique crescentic osteotomy is effective in the treatment of hallux valgus; its advantages over other procedures include its technical ease and low rate of complications.

Humeral shaft fractures secondary to throwing.

Twenty-seven male military recruits with humeral shaft fractures that occurred during throwing of a hand grenade were analyzed to determine the causes and contributing factors of this fracture in recreational pitchers. Average patient age was 22 years (range: 19-27 years). Objective criteria included type and fracture site on radiographs. Subjective data such as throwing style, previous pitching experience, and prodromal arm pain were obtained. The recruits' throwing style was deemed faulty. Analysis of the fracture configurations indicated an external rotation mechanism.