This article describes the effect of closed reduction and internal fixation with 3 different screw configurations for acute completely displaced femoral neck fractures in young adults. From 2001 to 2006, 136 patients (age range, 20-50 years) who had acute unilaterally completely displaced femoral neck fractures were evaluated retrospectively. All fractures were managed with closed reduction and internal fixation with 3 cannulated screws. The follow-up period was 55 months on average (range, 36-90 months). One hundred twenty-two patients were available for final evaluation of union condition and late complication. Twenty-three patients (18.9%) had nonunion, 15 (12.3%) had fixation failure, and 21 (17.2%) had avascular necrosis of the femoral head. The average duration from injury to surgery was 18.4 hours in the union group and 23.3 hours in the nonunion group, with no statistical significance (P=.196). The average duration from injury to surgery was 17.3 hours in the avascular necrosis of the femoral head group and 22.3 hours in the non-avascular necrosis of the femoral head group, with no statistical significance (P=.155). Vertical- and separated-type screw configurations resulted in a significantly higher nonunion rate (P=.001 and P=.0017, respectively) than parallel configuration. The complication rate in treating completely displaced femoral neck fractures with internal fixation in young adults is high, and screw configuration may further affect results.
Femoral neck fractures are commonly encountered in clinical practice. They are generally classified into undisplaced or displaced types.1 The treatment varies according to the fracture pattern, patient age, bone quality, and preexisting comorbidity.2-4 Closed or open reduction with internal fixation is generally used to treat displaced fractures in young patients and undisplaced fractures in patients of any age.5
Arthroplasty procedures for young adults with displaced fractures are not ideal because of the patients young age and high level of activity. The implants for fixation in such fractures include cannulated screws, sliding hip screw, nails, and pins.2,3,5-7 Traditionally, it has been advised to insert screws parallel to each other to provide compression across the fracture site and allow for some collapse to occur as the fracture heals.8-10 Previous reports have recommended positioning of the screws relative to each other within the femoral head, but few clinical-based studies were reported for young adults and none focused on displaced fractures in young adults.9,11-13
Displaced femoral neck fractures in young adults have a significant rate of poor outcomes due to higher incidences of complication, such as avascular necrosis of the femoral head14-20 and nonunion.14,15,18,21 To pursue an outcome with fewer complications, the initial fixation for fracture is undoubtedly important. The goal of this study was to evaluate the clinical and radiographic outcomes of closed reduction and internal fixation with cannulated screws for acute displaced femoral neck fractures in young adults. The effect of various factors, such as screw configuration, Pauwels classification, and fracture comminution, were evaluated in detail.
Materials and Methods
Between 2001 and 2006, 136 consecutive young patients (age range, 20-50 years) were treated at our institution for acute unilaterally completely displaced femoral neck fractures (Garden type 4 fractures without other associated ipsilateral femoral fracture) with closed reduction and internal fixation by three 7.0-mm (32-mm thread length) cannulated screws (Synthes, Solothurn, Switzerland) without washers.1,22 All of these surgeries were performed as soon as possible after diagnosis.
Intraoperatively, all fractures were reduced as anatomically as possible according to Gardens criteria by the senior authors (Y-P.S., C-M.C., F-Y.C.) and were fixed as rigidly as possible. All the screws were put in the head with the tip within 10 mm of the articular surface of the femoral head. The 3 cannulated lag screws were inserted in an inverted triangle configuration in all cases.4,23,24
All 136 patients were included in the initial evaluation of this retrospecetive study. Patients with prior history of hip fracture or hip joint arthritis of the fractured hip (2 patients), poor fracture reduction (3 patients), deep infection with late resection surgery (1 patient), and refracture due to a fall (1 patient), and patients lost follow-up due to various causes (7 patients) were excluded from the final evaluation. The remaining 122 patients (51 men, 71 women; 57 right hips, 65 left hips; mean age, 41.9 years [range, 20-50 years]) were included in the final evaluation. No history of immunological disease or steroid use was noted. The mechanism of injury was traffic accident in 102 patients, fall from height in 15, and miscellaneous causes in the remaining 5.
All surgeries were performed within 3 days of injury (average, 21.1 hours [range, 8-71 hours]). Intraoperatively, the reduction of all fractures met Gardens criteria (160°-180° in anteroposterior [AP] and lateral planes) after closed reduction. Fixation was performed via lateral approach with incisions between 3 and 5 cm in length. No open reduction or capsulotomy was done in this series.
Postoperatively, all patients had toe-touch weight bearing with a walker for 12 weeks, to advance to weight bearing thereafter. After discharge, each patient was followed once every 2 weeks in the first month and once every month thereafter. Additional visits were arranged if implicated. Radiographic and functional evaluations were done at every visit and once every 6 months after fracture union. Additional computed tomography (CT) scan was done in all cases of nonunion and suspected nonunion for confirmation, and additional bone scan was done in all cases of avascular necrosis of the femoral head and suspected avascular necrosis of the femoral head for confirmation.
Each patient had detailed records of their personal data, smoking and drinking habits, mechanism and associated condition of the injury, type and classification of the fracture (Garden and Pauwels), body mass index (BMI), American Society of Anesthesiologists (ASA) score, course of management (including timing of treatment, course of operation, operation time, length of hospital stay, early complication, late complication, and management of complication), condition and course of the fracture healing, and functional recovery.1,25 No steroid was used in any patient during treatment and follow-up. The follow-up period was 55 months on average (range, 36-90 months).
All AP and lateral radiographs taken in this series were standardized, and the AP views were taken with the hip straight on the table with 10° of internal rotation. In all patients, the inferior screw entered around or above the level of lesser trochanter within 1 cm of the inferior cortex of the femoral neck.26 The superior 2 screws entered in the mid-third area relative to the femoral neck. The screw configurations of all the patients were recognized in AP and lateral radiographic views. The screw configurations of 115 of the 122 patients were defined according to the angles formed between the 3 screws, comprising: (1) parallel (-2° to 2°); (2) parallel-divergent (>2°); (3) parallel-convergent (<2°); and (4) separated types (mixed type 2 and 3, with the upper 2 screws angled >4°) (Figure 1).
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|Figure 1: Parallel-convergent (A), parallel (B), parallel-divergent (C), and separated (D) screw configurations. Figure 2: A case of vertical screw configuration. |
In the lateral view of these 115 patients, the distance between the superior 2 screws were all at least half of the AP cortex length. In another 7 patients, the screw configuration was noted to be in a vertical line (not a triangular configuration) in the lateral view, and this was defined as vertical configuration (Figure 2). The position of each screw in the AP and lateral radiographs was expressed as a percentage of the maximum diameter of the femoral head. The distance from each screw tip to the joint was also evaluated on the AP radiographs.27 The outcomes of these 5 groups of configurations were recorded and compared. Singh index of contralateral hip, Pauwels classification, and posterior comminution of the fracture were also recorded.28-30
Fixation failure was defined as loss of fracture reduction (>20° change in angulation and/or >5 mm translation in AP or lateral views) or change in the angle between the fixation screws by >2°, or backing of the screws by >10 mm or perforation of the femoral head by the screws.22,31 Nonunion was defined as persistent fracture gap at 6 months postoperatively (confirmed by radiograph and CT), with or without failure of fixation. Avascular necrosis of the femoral head was defined as increased bone density with or without the sphericity of femoral head collapse (confirmed by radiograph and bone scan). None of the nonunion cases were included in the avascular necrosis of the femoral head group.
The presence of posterior comminution was assessed by the determination of fragmentation of the posteromedial cortex on radiographs at the time of admission and in the immediate postoperative period.21 The fracture classification (Garden and Pauwels), quality of reduction, status of posterior comminution, and screw configurations were evaluated by independent observers (H-K.H., C-L.L.) blinded to the eventual fracture healing outcome. In the Pauwel classification, the mean of angles measured on proximal and distal fracture surfaces in the postreduction AP radiograph was used. All the final evaluations were interpreted by 3 senior staff (Y-P.S., C-M.C., F-Y.C.).
All patients were measured for all response variables, which included demographic variables and important outcomes. Data were represented as mean and standard deviation for continuous response variables or percentages for discrete variables with respect to the 2 groups. Chi-square test was used to compare differences between the 2 groups for each discrete variable, and Student t test was used for each continuous variable. The P value was set before analysis at .05 for each test.
The angles between the screws in the 122 displaced fractures were measured, and the screw configurations were classified. The mean distance from screw tip to the hip joint for all the screws was 8.9 mm (range, 4.5-11.2 mm) in the failure group (both nonunion and fixation failure) and 9.5 mm (range, 4.5-12 mm) in the uneventfully healed group. The difference was not statistically significant (P=.341).
Twenty-three patients (18.9%) had nonunion, 15 (12.3%) had fixation failure, and 21 (17.2%) had avascular necrosis of the femoral head. The average duration from injury to operation was 18.4 hours in union group and 23.3 hours in nonunion group, with no statistical significance (P=.196). The average duration from injury to operation was 17.3 hours in the avascular necrosis of the femoral head group and 22.3 hours in non-avascular necrosis of the femoral head group, with no statistical significance (P=.155).
Radiographic results in each screw configuration are shown in Table 1. The correlations of sex, ASA score, BMI, smoking, alcohol drinking, Singh index, posterior comminution, and Pauwel classification to the radiographic results are shown in Tables 2 through 4.21 According to Pauwel classification, there were 16 type I fractures (13.1%), 77 type II fractures (63.1%), and 29 type III fractures (23.8%).
This study investigated the effect of closed reduction and internal fixation with 3 cannulated screws for acute completely displaced femoral neck fractures in young adults. The reported nonunion rate of displaced femoral neck fracture ranged from 10% to 30%, and the avascular necrosis of the femoral head rate ranged from 15% to 33%.32 The nonunion rate and avascular necrosis of the femoral head rate in our series were comparable to those in other reports, although no open reduction and capsulotomy was done in our cases.
The effectiveness of capsulotomy is still controversial. Some reports show that the decompression of intracapsular hematoma may prevent the development of avascular necrosis of the femoral head, but the disturbances of the vascularity of the femoral head by capsulotomy, and also the open reduction, raise concern.33-38 This is why we do not perform capsulotomy and open reduction in these injuries.
Another controversial factor is the timing of surgery. Some studies have shown possible benefits to early fixation, whereas other studies have not shown significant effects of early fixation on the development of nonunion and avascular necrosis of the femoral head.5,21,39-41 Our results showed that the timing of the surgery had no significant effect on the development of nonunion and avascular necrosis of the femoral head, although all the surgeries were performed within 72 hours of injury. However, we believe that it may be beneficial for these patients to receive early surgery; fracture pain and hospital stay could be shortened.
In this series of younger patients, sex, ASA score, BMI, smoking, alcohol drinking, and Singh index were shown to have no significant effect on the rate of nonunion, fixation failure with union, and avascular necrosis of the femoral head (Tables 2-4). Some studies show that smoking may impair the union of fracture, and others show that alcohol drinking may increase bone mineral density, and thus may improve bone union.42-50 These statements are not supported by our results, which may be due to the characteristics of younger age (good bone quality and high activity) in this study, and these characteristics may make the effects of smoking and drinking unimportant. However, the habits of smoking and alcohol consumption were not quantified in this study.
Pauwel type III fracture, posterior comminution, and combination of posterior comminution and Pauwel type III fracture were shown to have significantly adverse effects on the fixation and union of fractures, but not on avascular necrosis of the femoral head (Tables 2-4). These results were in accordance with other reports.6,7,27,51,52 Pauwel type III fractures and comminution of the posteromedial cortex of the femoral neck occur high in displaced femoral neck fractures, and these conditions are important risk factors of insecure fixation and nonunion.6,7,19,35,36 No definite risk factors could be found for the development of avascular necrosis of the femoral head in this series of displaced femoral neck fracture in young adults.
Several reports suggest that parallel screws in subchondral fixation for femoral neck fracture would improve the overall stability of fixation if the reduction was adequate.53-57 In our study, we analyzed the results of 5 types inverted-triangular screw configurations for fixation of displaced femoral neck fracture. It was shown that the complication rates of different groups of screw configuration, in order of increment, were lowest in the parallel screw configuration, then the parallel-divergent screw configuration, the parallel-convergent configuration, and the separated screw configuration, and were highest in the vertical screw configuration (Table 1). The nounion rates of the separated screw and vertical screw configurations were significantly higher than those of the parallel screw configuration. These results may be due to the best sliding compression effect of the fracture sites in the parallel screw configuration.
New bone bridging is difficult without adequate compression of the fracture sites, and then fracture gap appears after osteoclasts functioning in the process of bone union.58,59 Our results supported the recommendation of Selvan et al24 that configuration of 2 or 3 vertical screws should be avoided and the parallel triangular configuration can provide stronger stability. In our series, the 7 cases of 3 vertical screw configurations were found to have the highest failure rate, and such a high failure could be due to the lack of 3-dimensional fixation in this kind of screw configuration.
The main causes of failing to achieve appropriate screw configuration could be a less meticulous technique or unwillingness to repeat guide pin insertion, which should be avoided.
The main limitations of this study are its retrospective nature and small patient numbers, and thus some bias of evaluation could not be avoided completely.
- Caviglia HA, Osorio PQ, Comando D. Classification and diagnosis of intracapsular fractures of the proximal femur. Clin Orthop Relat Res. 2002; (399):17-27.
- Hedlund R, Lindgren U, Ahlbom A. Age- and sex-specific incidence of femoral neck and trochanteric fractures. An analysis based on 20,538 fractures in Stockholm County, Sweden, 1972-1981. Clin Orthop Relat Res. 1987; (222):132-139.
- Bjørgul K, Reikerås O. Hemiarthroplasty in worst cases is better than internal fixation in best cases of displaced femoral neck fractures: a prospective study of 683 patients treated with hemiarthroplasty or internal fixation. Acta Orthop. 2006; 77(3):368-374.
- Bjørgul K, Reikerås O. Outcome of undisplaced and moderately displaced femoral neck fractures. Acta Orthop. 2007; 78(4):498-504.
- Raaymakers EL. Fractures of the femoral neck: a review and personal statement. Acta Chir Orthop Trauma Cech. 2006; 73(1):45-59.
- Aminian A, Gao F, Fedoriw WW, Zhang LQ, Kalainov DM, Merk BR. Vertically oriented femoral neck fractures: mechanical analysis of four fixation techniques. J Orthop Trauma. 2007; 21(8):544-548.
- Liporace F, Gaines R, Collinge C, Haidukewych GJ. Results of internal fixation of Pauwels type-3 vertical femoral neck fractures. J Bone Joint Surg Am. 2008; 90(8):1654-1659.
- Madsen F, Linde F, Andersen E, Birke H, Hvass I, Poulsen TD. Fixation of displaced femoral neck fractures. A comparison between sliding screw plate and four cancellous bone screws. Acta Orthop Scand. 1987; 58(3):212-216.
- Paus A, Gjengedal E, Hareide A, Jørgensen JJ. Dislocated fractures of the femoral neck treated with von Bahr screws or hip compression screw. Results of a prospective, randomized study. J Oslo City Hosp. 1986; 36(5-6):55-61.
- Rehnberg L, Olerud C. Fixation of femoral neck fractures. Comparison of the Uppsala and von Bahr screws. Acta Orthop Scand. 1989; 60(5):579-584.
- Asnis SE, Wanek-Sgaglione L. Intracapsular fractures of the femoral neck. Results of cannulated screw fixation. J Bone Joint Surg Am. 1994; 76(12):1793-1803.
- Lagerby M, Asplund S, Ringqvist I. Cannulated screws for fixation of femoral neck fractures. No difference between Uppsala screws and Richards screws in a randomized prospective study of 268 cases. Acta Orthop Scand. 1998; 69(4):387-391.
- Lykke N, Lerud PJ, Strømsøe K, Thorngren KG. Fixation of fractures of the femoral neck. A prospective, randomised trial of three Ullevaal hip screws versus two Hansson hook-pins. J Bone Joint Surg Br. 2003; 85(3):426-430.
- Protzman RR, Burkhalter WE. Femoral-neck fractures in young adults. J Bone Joint Surg Am. 1976; 58(5):689-695.
- Dedrick DK, Mackenzie JR, Burney RE. Complications of femoral neck fracture in young adults. J Trauma. 1986; 26(10):932-937.
- Zetterberg CH, Irstam L, Andersson GB. Femoral neck fractures in young adults. Acta Orthop Scand. 1982; 53(3):427-435.
- Swiontkowski MF, Winquist RA, Hansen ST Jr. Fractures of the femoral neck in patients between the ages of twelve and forty-nine years. J Bone Joint Surg Am. 1984; 66(6):837-846.
- Kofoed H. Femoral neck fractures in young adults. Injury. 1982; 14(2):146-150.
- Lee CH, Huang GS, Chao KH, Jean JL, Wu SS. Surgical treatment of displaced stress fractures of the femoral neck in military recruits: a report of 42 cases [published online ahead of print September 2, 2003]. Arch Orthop Trauma Surg. 2003; 123(10):527-533.
- Haidukewych GJ, Rothwell WS, Jacofsky DJ, Torchia ME, Berry DJ. Operative treatment of femoral neck fractures in patients between the ages of fifteen and fifty years. J Bone Joint Surg Am. 2004; 86(8):1711-1716.
- Upadhyay A, Jain P, Mishra P, Maini L, Gautum VK, Dhaon BK. Delayed internal fixation of fractures of the neck of the femur in young adults. A prospective, randomised study comparing closed and open reduction. J Bone Joint Surg Br. 2004; 86(7):1035-1040.
- Zlowodzki M, Weening B, Petrisor B, Bhandari M. The value of washers in cannulated screw fixation of femoral neck fractures. J Trauma. 2005; 59(4):969-975.
- Oakey JW, Stover MD, Summers HD, Sartori M, Havey RM, Patwardhan AG. Does screw configuration affect subtrochanteric fracture after femoral neck fixation? Clin Orthop Relat Res. 2006; (443):302-306.
- Selvan VT, Oakley MJ, Rangan A, Al-Lami MK. Optimum configuration of cannulated hip screws for the fixation of intracapsular hip fractures: a biomechanical study. Injury. 2004; 35(2):136-141.
- American Society of Anesthesiologists. New classification of physical status. Anesthesiology. 2009; (24):111.
- Lindequist S. Cortical screw support in femoral neck fractures. A radiographic analysis of 87 fractures with a new mensuration technique. Acta Orthop Scand. 1993; 64(3):289-293.
- Gurusamy K, Parker MJ, Rowlands TK. The complications of displaced intracapsular fractures of the hip: the effect of screw positioning and angulation on fracture healing. J Bone Joint Surg Br. 2005; 87(5):632-634.
- Scheck M. The significance of posterior comminution in femoral neck fractures. Clin Orthop Relat Res. 1980; (152):138-142.
- Stiasny J, Dragan S, Kulej M, Martynkiewicz J, Plochowski J, Dragan SL. Comparison analysis of the operative treatment results of the femoral neck fractures using side-plate and compression screw and cannulated AO screws. Orthop Traumatol Rehabil. 2008; 10(4):350-361.
- Bartonícek J. Pauwels classification of femoral neck fractures: correct interpretation of the original. J Orthop Trauma. 2001; 15(5):358-360.
- Alho A, Benterud JG, Solovieva S. Internally fixed femoral neck fractures. Early prediction of failure in 203 elderly patients with displaced fractures. Acta Orthop Scand. 1999; 70(2):141-144.
- Damany DS, Parker MJ, Chojnowski A. Complications after intracapsular hip fractures in young adults. A meta-analysis of 18 published studies involving 564 fractures. Injury. 2005; 36(1):131-141.
- Alberts KA, Jervaeus J. Factors predisposing to healing complications after internal fixation of femoral neck fracture. A stepwise logistic regression analysis. Clin Orthop Relat Res. 1990; (257):129-133.
- Bonnaire F, Schaefer DJ, Kuner EH. Hemarthrosis and hip joint pressure in femoral neck fractures. Clin Orthop Relat Res. 1998; (353):148-155.
- Crawfurd EJ, Emery RJ, Hansell DM, Phelan M, Andrews BG. Capsular distension and intracapsular pressure in subcapital fractures of the femur. J Bone Joint Surg Br. 1988; 70(2):195-198.
- Maruenda JI, Barrios C, Gomar-Sancho F. Intracapsular hip pressure after femoral neck fracture. Clin Orthop Relat Res. 1997; (340):172-180.
- Harper WM, Barnes MR, Gregg PJ. Femoral head blood flow in femoral neck fractures. An analysis using intra-osseous pressure measurement. J Bone Joint Surg Br. 1991; 73(1):73-75.
- Strömqvist B, Nilsson LT, Egund N, Thorngren KG, Wingstrand H. Intracapsular pressures in undisplaced fractures of the femoral neck. J Bone Joint Surg Br. 1988; 70(2):192-194.
- Butt MF, Dhar SA, Gani NU, et al. Delayed fixation of displaced femoral neck fractures in younger adults [published online ahead of print January 31, 2008]. Injury. 2008; 39(2):238-243.
- Ly TV, Swiontkowski MF. Treatment of femoral neck fractures in young adults. Instr Course Lect. 2009; (58):69-81.
- Tian W, Cui Z, Kan S. Comparison of cannulated screws fixation with different reduction methods at different time points for displaced femoral neck fractures in terms of fracture healing [in Chinese]. Zhongguo Xiu Fu Chong Jian Wai Ke Za Zhi. 2009; 23(4):440-443.
- Schmitz MA, Finnegan M, Natarajan R, Champine J. Effect of smoking on tibial shaft fracture healing. Clin Orthop Relat Res. 1999; (365):184-200.
- Kyrö A, Usenius JP, Aarnio M, Kunnamo I, Avikainen V. Are smokers a risk group for delayed healing of tibial shaft fractures? Ann Chir Gynaecol. 1993; 82(4):254-262.
- Ly TV, Swiontkowski MF. Treatment of femoral neck fractures in young adults. J Bone Joint Surg Am. 2008; 90(10):2254-2266.
- Pape HC, Krettek C, Friedrich A, Pohlemann T, Simon R, Tscherne H. Long-term outcome in children with fractures of the proximal femur after high-energy trauma. J Trauma. 1999; 46(1):58-64.
- Castillo RC, Bosse MJ, MacKenzie EJ, Patterson BM; LEAP Study Group. Impact of smoking on fracture healing and risk of complications in limb-threatening open tibia fractures. J Orthop Trauma. 2005; 19(3):151-157.
- Chen F, Osterman AL, Mahony K. Smoking and bony union after ulna-shortening osteotomy. Am J Orthop (Belle Mead NJ). 2001; 30(6):486-489.
- Wosje KS, Kalkwarf HJ. Bone density in relation to alcohol intake among men and women in the United States [published online ahead of print November 8, 2006]. Osteoporos Int. 2007; 18(3):391-400.
- Hodges DL, Kumar VN, Redford JB. Effects of alcohol on bone, muscle and nerve. Am Fam Physician. 1986; 34(5):149-156.
- Matsuo K, Hirohata T, Sugioka Y, Ikeda M, Fukuda A. Influence of alcohol intake, cigarette smoking, and occupational status on idiopathic osteonecrosis of the femoral head. Clin Orthop Relat Res. 1988; (234):115-123.
- Kauffman JI, Simon JA, Kummer FJ, Pearlman CJ, Zuckerman JD, Koval KJ. Internal fixation of femoral neck fractures with posterior comminution: a biomechanical study. J Orthop Trauma. 1999; 13(3):155-159.
- Baitner AC, Maurer SG, Hickey DG, et al. Vertical shear fractures of the femoral neck. A biomechanical study. Clin Orthop Relat Res. 1999; (367):300-305.
- Stankewich CJ, Chapman J, Muthusamy R, et al. Relationship of mechanical factors to the strength of proximal femur fractures fixed with cancellous screws. J Orthop Trauma. 1996; 10(4):248-257.
- Elmerson S, Andersson GB, Pope MH, Zetterberg C. Stability of fixation in femoral neck fractures. Comparison of four fixation devices in vivo and in cadavers. Acta Orthop Scand. 1987; 58(2):109-112.
- Parker MJ, Porter KM, Eastwood DM, Schembi Wismayer M, Bernard AA. Intracapsular fractures of the neck of femur. Parallel or crossed garden screws? J Bone Joint Surg Br. 1991; 73(5):826-827.
- Martens M, Van Audekercke R, Mulier JC, Stuyck J. Clinical study on internal fixation of femoral neck fractures. Clin Orthop Relat Res. 1979; (141):199-202.
- Rubin R, Trent P, Arnold W, Burstein A. Knowles pinning of experimental femoral neck fractures: biomechanical study. J Trauma. 1981; 21(12):1036-1039.
- Shih CH, Wang KC. Femoral neck fractures. 121 cases treated by Knowles pinning. Clin Orthop Relat Res. 1991; (271):195-200.
- Clark DI, Crofts CE, Saleh M. Femoral neck fracture fixation. Comparison of a sliding screw with lag screws. J Bone Joint Surg Br. 1990; 72(5):797-800.
Drs Huang, Su, Chen, Chiu, and Liu are from the Department of Orthopedics and Traumatology, Taipei Veterans General Hospital, and Drs Chen, Chiu, and Liu are also from National Yang-Ming University, Taipei, Taiwan.
Drs Huang, Su, Chen, Chiu, and Liu have no relevant financial relationships to disclose.
Correspondence should be addressed to: Fang-Yao Chiu, MD, Department of Orthopedics and Traumatology, Taipei Veterans General Hospital, 201, Sec 2, Shih-Pai Rd, Taipei 112, Taiwan (email@example.com).