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Management of Femoral Neck Stress Fractures
Management of Femoral Neck Stress Fractures John B. Sledge III, MD Stress fractures are caused by repetitive submaximal loading of bone that causes microtrauma, where the bone either temporally or biomechanically does not have the ability to recover before repeated loading. Stress fractures are being diagnosed more frequently as the result of increased surveillance on the part of the physician and increased prevalence on the part of the patient. The diagnosis is made by a combination of history, physical examination, and imaging. Magnetic resonance imaging is the imaging modality of choice, after plain films, because of its greater specificity and sensitivity. Stress fractures are classified based on their cause, their location, their severity, their risk of progression, and the appearance of the fracture line. Treatment of femoral neck stress fractures is based on the duration of symptoms, the fracture classification, and the patient’s expectations. Treatment starts with activity modification and progresses to cannulated screws, sliding hip screw, blade plate, and/or intertrochanteric osteotomy. Predictors of successful surgical outcomes are accurate fracture classification, early anatomic reduction, addressing of any varus deformity in the reduction or the native neck, and placing the fracture line as horizontal as reasonable when performing an osteotomy. Mild fractures in the recreational athlete will lead to a period of decreased activity, rapid healing, and return to full activity, whereas more severe fractures will require more intervention and a longer recovery period. Displaced fractures have a high rate of avascular necrosis, pseudoarthrosis, refracture, and progressive arthrosis. Elite athletes require aggressive management and, even then, are unlikely to return to their previous professional level. Oper Tech Sports Med 14:265-269 © 2006 Elsevier Inc. All rights reserved. KEYWORDS stress fracture, femoral neck, treatment, review, imaging, diagnosis, complications
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tress fractures of the femoral neck are being diagnosed with increased frequency as the result of an increased prevalence in the population, increased suspicion on the part of the practitioner, and better imaging modalities. Femoral neck stress fractures have long been a recognized issue with new military recruits,1 and with both an increase in the activity level and in the age of our patients, it has become more common in recreational and elite athletes.2,3 Stress fractures accounts for 50% of new hip pain in military recruits and 10% of new hip pain in recreational athletes. These injuries are seen in 3 distinct patient populations: (1) young, healthy, active individuals such as recreational runners, endurance athletes, or military recruits; (2) individuals with metabolic bone disease from either intrinsic factors such as hormonal
Clinical Associate in Orthopaedics, Massachusetts General Hospital, Boston, MA. Address reprint requests to John B. Sledge III, MD, Sports Medicine North Orthopaedic Surgery, Inc, One Orthopedics Drive, Peabody, MA 01960. E-mail: [email protected]
1060-1872/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.otsm.2006.10.002
imbalance or extrinsic factors such as steroid use; and (3) elderly who have osteoporosis.4 Stress fractures are part of a diagnostic continuum that has stress fractures on one end and insufficiency fractures on the other. They both have a common final biomechanical pathway in which the repetitive stress on the bone is greater than the bone’s biological ability to sustain the load and/or repair the micro trauma. We will focus our discussion primarily on stress fractures, but most patients will have some degree of both. The level of patient activity usually is the determining variable between the two. New military recruits who develop femoral neck fractures during boot camp are on one end of the spectrum and patients with osteoporosis, hyperparathyroidism, or metabolic bone disease are on the other end. The amenorrheic woman who develops a stress fracture during routine sports has a combination of both. There are grades of patient susceptibility and grades of increased activity. It is the imbalance between the level of activity and the bone’s inherent strength and reparative capabilities that lead to a fracture. Whether it is described as an insufficiency fracture or as a stress fracture depends on whether the activity level or the 265
266 quality of the bone is the major causative fracture. Initial treatment does not differentiate between the 2 causes because surgery and activity modification are treatments for both. Early diagnosis is paramount in the management of both fractures. Fortunately, a delay in the diagnosis and treatment of stress fractures is less common now then it was as a result of an increase in suspicion and better imaging, but when the diagnosis is missed or delayed, there is at best a delay in the patient’s return to activity and at worst a progression to a displaced fracture. Nondisplaced femoral neck stress fractures have a very low rate of avascular necrosis, nonunion, and varus deformity, but these are all risks with displaced fractures. The femoral neck accounts for roughly 50% of all stress fractures, whereas it accounts for only 10% of insufficiency fractures.5 When a stress fracture of the femoral neck is diagnosed, it is important to identify any potential causes of insufficiency and other injury sites.
Risk Factors The most common cause, and therefore the greatest risk factor, is a sudden increase in physical activity, namely running. In a 70-month screening process performed on Finnish military recruits, 85 patients with 92 fatigue injuries were discovered, giving an incidence of 99 per 100,000 personyears.6 In a separate Finnish Military study, 179 recruits were studied at the very beginning of their military service. During the year-long commitment of their service, 15 men experienced stress fractures, with 13 occurring in the first 6 months and 2 occurring in the second 6 months. Tall height, poor physical condition, low hip bone mineral content (BMC), low hip bone mineral density (BMD), and high parathyroid hormone levels were risk factors for stress fractures.7 The lower occurrence in the second 6-month period was attributed to improvements in the recruits’ physical condition, BMC, and BMD, and the fact that those most susceptible to sustaining a fracture had also been selected out by having had one in the first 6 months.7 Exercise is great at increasing bone mass and decreasing the risk for stress fractures, but too much exercise without allowing for bony adaptation is the most common cause of stress fractures. Exercise increases both the bone mass and the bending rigidity of the femoral neck in women between the ages of 18 to 31.8 This increase would theoretically protect women in the same way as it has been shown to protect men.7 The use of oral contraception has been shown to partially mitigate the beneficial effects of exercise.8 There are multiple reports of amenorrheic female athletes being at increased risk for stress fractures in the femoral neck and elsewhere.9,10 Thirty-three military recruits with femoral neck stress fractures had a lower bone mineral density than did 15 patients undergoing treatment for scaphoid nonunions who were used as controls. Although rates of BMD were lower in the stress fracture group, no consistent histomorphometric differences were noted on analysis of the iliac crest, and no patient had osteoporosis.11 When BMD has been used as a screening tool in the initial pool of military recruits, it has not
J.B. Sledge III shown to be a useful predictor; that is to say that people who develop stress fractures have a lower BMD than those who do not, but of the initial recruits that had a low BMD, more did not get fractures than did.7,11,12 Proximal femoral morphology has been thought to play a role in a patient’s susceptibility in developing a stress fracture. The thought has been that a varus neck shaft angle in combination with the hip girdle muscle will increase the tensile forces on the lateral side of the femoral neck and will increase the compressive forces on the medial side. These effects can also be accentuated by an increase in the lateral offset of the proximal femur. Increasing either the varus angle or the lateral offset will increase the torque and/or sheer across the femoral neck. There is some evidence to support this position in that military recruits with coxa vara have a greater incidence and an earlier presentation of stress fractures than the recruits with normal neck shaft angles.7 In a Spanish retrospective assessment, 12 patients with varus femoral necks and stress fractures were paired with 10 patients who had stress fractures and normal neck shaft angles.13 Evaluation showed that patients in the coxa vara group presented at an earlier age, had a longer duration of symptoms and required less of an increase in their activity level to put them at risk.
Presentation and Diagnosis Stress fractures are common overuse injuries seen in athletes and military recruits. The pathogenesis is multifactorial and involves an alteration in the patient’s activity level or in their bone quality. An increase in repetitive submaximal stresses on normal bone is the most common cause, although intrinsic and extrinsic factors such as nutritional status, use of antiinflammatory drugs, radiation, osteoporosis, or hormonal imbalance may contribute to the onset of stress fractures.3 The classic presentation is a patient who experiences the insidious onset of pain after an abrupt increase in the duration or intensity of activity. With femoral neck stress fractures, this often presents with a gradual onset of activity induced anterior hip and thigh pain. Patients often have a hard time localizing the symptoms and can complain of posterior hip pain, lateral hip pain and referred knee pain. Laboratory values are routinely normal. Extensive preactivity blood work in military recruits have not yielded any predictors of stress fractures.7 As mentioned previously, some of the laboratory values were lower in the fracture group then in the control group, but all values were still within the normal range and did not offer any predictive value. An accurate and thorough history in association with sequential radiographs often will suffice to make the diagnosis. This is particularly true when the diagnostic triad are present—a history of recent increase in abnormal repetitive stress, pain increasing with activity and diminishing with rest, and pain in one of the common locations (anterior tibia, metatarsals, calcaneus or femoral neck).14 Bone scan, magnetic resonance imaging (MRI) and occasionally computed tomography (CT) are used for patients presenting with atyp-
Management of femoral neck stress fractures ical exams. Imaging studies are the key to the definitive diagnosis. Plain films often are negative but occasionally will show the classic stress fracture, subperiostial callus, or intraosseous sclerosis. In a series of 60 fractures, plain films showed changes in 39 patients (65%), bone scan was positive in 21 of 24 cases (87%), and CT was positive in 54 of 55 cases (98%).5 Although CT was more accurate than the bone scan at identifying the primary fracture, it was not the imaging modality recommended by the authors because, in this series, when both insufficiency fractures and stress fractures were included, the bone scans identified 31 other noncontiguous fractures. The authors concluded that because radiography signs are inconsistent and because CT can only recognize the primary fracture, that scintigraphy is the imaging modality of choice in patients with a diagnosis of an insufficiency fracture (note: MRI was not used during this study). MRI can detect the early changes of osseous stress injury and can differentiate these from the changes associated with transient osteoporosis. Bone scan alone or more frequently in conjunction with MRI is the recommendation in patients with insufficiency fractures.5 MRI was used to assess the time to resolution of the signal abnormality, with 9 of 10 patients showing resolution of abnormal MR signal intensity on STIR imaging within 6 months of initiating treatment for femoral neck stress fractures.15 Because of the several reports in the literature of MRI documented stress fractures that were not seen with bone scans, the ability of MRI to define the extent of the injury and to be used to assess recovery has made it the imaging modality of choice and scintigraphy has taken a secondary role.14,16 MRI is the modality of choice for differentiating the cause of hip pain in the athlete, including the diagnosis of femoral neck stress fractures. In 19 military recruits with hip pain, bone scan had an accuracy of 68% and a falsepositive rate of 32%.17 The patients then underwent MRI, which was able to differentiate femoral neck stress fractures from muscle injury, tendonitis, avascular necrosis (AVN), unicameral bone cyst, and labral pathology.17,18 MRI has proven to be superior to CT and bone scan in providing early and accurate assessment of the cause of hip pain in young adults.
Classification Stress fractures are classified based on their cause, their location, their severity, their risk of progression, and the appearance of the fracture line. Fractures that are more attributable to excessive repetitive submaximal impact are termed stress fractures, while those more attributable to a decrease in the inherent biomechanical capabilities of the bone are deemed insufficiency fractures. Fractures that occur on the tension side of a bone are aptly called tension fractures, whereas those occurring on the compression side of the bone are appropriately called compression fractures. There was an early attempt to classify stress fractures by their radiographic appearance. This has now been modified to include MRI findings as well.19 Type 1 fractures are MRI-
267 positive fractures, which radiographically may show endosteal or periosteal callus without an overt fracture line. Type 2 fractures radiographic show a nondisplaced fracture line. Type 3 fractures show a displaced fracture line. Some authors have described an MRI finding that they have termed a stress reaction and have hypothesized that this is a precursor to a stress fracture.4 Early in a patient’s course, it is difficult to determine the clinical significance of some MRI findings because of MRI’s sensitivity to marrow changes and the numerous and complex adaptive ways bone can respond to overuse. Fractures have been classified based on their risk of progression or of serious complications. Low-risk fractures are usually those that are type 1 or 2 fractures that are on the compression side of the bone, as they have a low probability for becoming displaced, and a low incidence of serious complication such as pseudoarthrosis, AVN, refracture, progressive arthrosis, or persistent pain. High-risk fractures are just the opposite and are an orthopedic emergency, requiring prompt surgical intervention.1 High-risk tension fracture sites are the femoral neck, the patella, the anterior cortex of the tibia, the medial malleolus, the talus, the tarsal navicular, the fifth metatarsal, and the great toe sesamoids.3,20
Treatment The treatment of femoral neck stress fractures is based on the duration of symptoms, the fracture classification, and the patient’s expectations. One must always look for associated factors, such as metabolic, intrinsic and extrinsic, and treat these contributing variables in conjunction with treating the fracture. If there has been a recent change in the frequency, duration, or intensity of exercise, then activity modification is the initial treatment of low-risk fractures. All stress fractures initially should be treated aggressively because undertreated high-risk fractures can have devastating consequences, but even neglected low-risk femoral neck stress fractures are a challenge to treat, requiring prolonged treatment, extended convalescence, and potentially poor outcome.2 The initial treatment for all stress fractures is activity modification to eliminate all activities causing pain. If the symptoms are only there after sporting or training activities, then only these need to be avoided. If the pain is also present with day-to-day ambulation, then the patient must be made nonweight-bearing. On rare occasions, the symptoms are bilateral, and a wheelchair needs to be used. The return to exercise can parallel the resolution of symptoms and the loss of marrow signal changes on the MRI. When the symptoms have subsided, it is important to put patients through a supervised reconditioning program, as they have just been deconditioned and their tendency is to return back to their previous activity level. A closed-chain activity program has been suggested by many to initially avoid impact loading, with progression to running as the last step. The surgical treatments available are pinning, sliding hip screw, blade plate, and intertrochanteric osteotomy. Although the literature has no comparative studies and the choice often falls to the surgeon’s preference, the reported
268 series do give us some guidance in certain circumstances. First, classify the fracture as discussed previously and look for and start treatment on any identifiable contributing metabolic cause. High-risk fractures and those in elite athletes need to be treated more aggressively then low-risk fractures in recreational athletes. Stress reactions on MRI and low-risk type 1 fractures that do not respond to activity modification may be treated with multiple pins. It is important to use 3 pins that are placed in an inverted triangle with the single inferior screw being placed right along the medial calcar. Low-risk type 2 fractures have the greatest variability and the least consensus on treatment. Small type 2 fractures have been treated successfully with multiple pins. There are reports of successfully treated type 2 fractures with sliding hip screw or blade plate, although these had a higher complication rate then did multiple pins.21 From the selection methods reported, it cannot be determined whether this was the result of implant selection or patient selection. We do not presently use either sliding hip screw or blade plates alone for the treatment of larger low-risk type 2 fractures. Small type 2 fractures with a normal neck angle are treated with multiple pins. Small type 2 fractures with a varus neck or a vertical fracture line and all large type 2 fractures are usually treated with an intertrochanteric osteotomy. There are exceptions such as type 2 fractures with more horizontal fracture lines in recreational athletes who have no pain with ambulation and are willing to give up return to their sport. High-risk type 2 fractures routinely are treated with intertrochanteric osteotomy. My preference is to use the highangle blade plate because it removes less bone, controls rotation, allows for plate assisted reduction techniques, and has better apposition to the lateral side of the femur after the osteotomy. The technique for the osteotomy has been well characterized by both Ballmar and Muller.22,23 Displaced fractures, type 3 fractures, are a surgical emergency and require immediate reduction and internal fixation. Greater than a 24-hour delay has been shown to correlate with a worse prognosis.12 We obtain CT scans on our displaced fractures if there is any question as to fracture pattern, extent or orientation. The outcome of displaced fractures is variable, but a decreased time to reduction and an increased quality of the reduction are consistently correlated with decreased complications (AVN, refracture, pseudoarthrosis and progressive arthrosis) and improved functional outcome.2,12,24,25 If after a reduction is obtained, there is a residual varus alignment or if the fracture line is vertical then consideration should be given to performing an osteotomy at the time of the reduction. The importance of opening the capsule to decompress the hematoma is unclear at this time. With displaced fractures since there is no literature evidence, I will routinely open the capsule anteriorly to help stabilize the head and to assess the quality of the reduction.
Outcome Displaced fractures have a significantly worse prognosis and greater complication rate than nondisplaced fractures and
J.B. Sledge III this has been the topic of most reported series.2 Cannulated screw fixation with fibular graft in patients ages 18 to 50 with displaced femoral neck fractures showed only a 90.6% fusion rate and even these showed a decreased Harris Hip score of only 87.1.2 In another study, 42 patients with displaces fractures were treated with either a compression hip screw (17 cases) or multiple cancellous screws (25 cases). Ten patients developed AVN at average follow-up of 5.6 years. Risk factors identified for the development of AVN were delay in reduction and fixation (1.5 days versus 5.9 days), postoperative varus alignment, and the use of screws.12 Of the 42 patients 71% had good-to-excellent results, 9.5% had acceptable results, and 19% had poor results. Eight patients required prosthetic replacements. In 12 surgically treated displaced femoral neck fractures in young male military recruits, AVN developed in 5. These patients were treated early with a sliding hip screw in 10 cases and either a Jewett nail or an OA 130° blade plate in the other 2. Nonunion developed in 3 cases, 2 of whom later went on to develop AVN. Only 6 patients (50%) were scored as good or excellent at follow-up.26 A series of 25 patients who were treated nonoperatively were contacted retrospectively 5 to 7 years after their diagnosis.25 No patient had developed AVN, nonunion, valgus deformity, or posttraumatic arthritis. On self-administered outcome measures, 68% of patients felt “somewhat bothered” in at least one functional category on the Musculoskeletal Function Assessment, and 9 patients (36%) felt “disabled.” There was no correlation between fracture location (tension of compression), treatment method, or BMD. This series demonstrates that even in patients whose diagnosis was timely, their treatment appropriate and no major complications, that the long-term outcome for these patients is often not a return to normal function. A report of college athletes and runners showed that with nondisplaced, low-risk, compression type femoral neck fractures with early diagnosis and treatment with nonweightbearing activity followed by activity modification, there was excellent healing.19 The patients were separated into 2 groups: recreational athletes and elite athletes. There was a significant difference in ability to return to sports in that none of the elite athletes were able to return to their previous level of performance. In 23 patients followed up at an average of 6.5 years after their diagnosis, the patients’ outcome correlated with fracture type and duration of symptoms.27 Seven patients with type 1 fractures (positive MRI, but no fracture line on plain film) that were diagnosed with less than 6 months of symptoms were all treated with activity modifications. All but 1 healed without incident, whereas 1 progressed and required surgical intervention. Of the remaining 16 patients treated surgically, 6 required repeat operations. Of the 6, 5 had type 3 fractures (displaced) and 1 had a type 2 fracture (nondisplaced visible fracture). Reoperation was required for AVN in 3, pseudoarthrosis in 2, and refracture in 1. At follow-up, the overall results were good to excellent in 14 and bad or fair in 9. When tension side fractures were removed from the analysis, there was a trend toward more severe fractures, as measured
Management of femoral neck stress fractures by fracture type, as the duration of the patient’s symptoms increased.27
Summary Stress fractures are being diagnosed more frequently as the resulf of our increased suspicion and their increasing prevalence. The history and physical examination will usually place stress fractures on the differential diagnosis, and the situation is further clarified by an assessment of the potential intrinsic and extrinsic contributing factors. Plain radiographs will often confirm the diagnosis, but if not further imaging will be required. If an insufficiency fracture is suspected then MRI and bone scan should be considered, but if a stress fracture is more likely then just MRI will suffice. If the fracture is displaced I prefer a CT instead of the MRI. With imaging, the fracture can be classified and, in conjunction with the patient’s expectations, an appropriate treatment course can be selected. Improved outcomes largely depend on shorter duration of symptoms, shorter times to diagnosis, low-risk fractures, lesser fracture type and appropriate treatment. When surgery is performed the goals are rapid identification of the fracture, early anatomic reduction, removal of varus neck angle and placement of the fracture line in as horizontal an orientation as reasonable. Mild fractures in the recreational athlete will lead to a period of decreased activity, rapid healing, and return to full activity. More severe fractures will require more intervention and a significantly longer interruption in their activities. It is crucial that the treating physician focus on the long term outcome and inform the patient that this will require 6 to 18 months of treatment before full activity can be reinitiated. It is unlikely that elite or professional athletes or those with highrisk fractures will be able to return to their careers.
References 1. Jean JL, Lee GH, Tang HL, et al: Stress fracture of the femoral neck in young adult: report of four cases. Chang Gung Med J 3:188-195, 2001 2. Roshan A, Ram S: Early return to function in young adults with neglected femoral neck fractures. Clin Orthop Relat Res 447:152-7, 2006 3. Boden BP, Osbahr DC: High-risk stress fractures: evaluation and treatment. J Am Acad Orthop Surg 6:344-353, 2000 4. Egol KA, Koval KJ, Kummer F, et al: Stress fractures of the femoral neck. Clin Orthop Relat Res 348:72-78, 1998 5. Soubrier M, Dubost JJ, Boisgard S, et al: Insufficiency fracture. A survey of 60 cases and review of the literature. Joint Bone Spine 3:209-218, 2003 6. Niva MH, Kiuru MJ, Haataja R, et al: Fatigue injuries of the femur. J Bone Joint Surg Br 10:1385-1390, 2005
269 7. Valimaki VV, Alfthan H, Lehmuskallio E, et al: Risk factors for clinical stress fractures in male military recruits: a prospective cohort study. Bone 2:267-273, 2005 8. Burr DB, Yoshikawa T, Teegarden D, et al: Exercise and oral contraceptive use suppress the normal age-related increase in bone mass and strength of the femoral neck in women 18-31 years of age. Bone 6:855863, 2000 9. Voss L, DaSilva M, Trafton PG: Bilateral femoral neck stress fractures in an amenorrheic athlete. Am J Orthop 11:789-792, 1997 10. Leinberry CF, McShane RB, Stewart WG Jr., et al: A displaced subtrochanteric stress fracture in a young amenorrhiec athlete. Am J Sports Med 4:485-487, 1992 11. Muldoon MP, Padgett DE, Sweet DE, et al: Femoral neck stress fractures and metabolic bone disease. J Orthop Trauma 3:181-185, 2001 12. Lee CH, Huang GS, Chao KH, et al: Surgical treatment of displaced stress fractures of the femoral neck in military recruits: a report of 42 cases. Arch Orthop Trauma Surg 10:527-533, 2003 13. Carpintero P, Leon F, Zafra M, et al: Stress fractures of the femoral neck and coxa vara. Arch Orthop Trauma Surg 6:273-277, 2003 14. Wen DY, Propeck T, Singh A: Femoral neck stress injury with negative bone scan. J Am Board Fam Pract 2:170-174, 2003 15. Slocum KA, Gorman JD, Puckett ML, et al: Resolution of abnormal MR signal intensity in patients with stress fractures of the femoral neck. AJR Am J Roentgenol 5:1295-1299, 1997 16. Spitz DJ, Newberg AH: Imaging of stress fractures in the athlete. Radiol Clin North Am 2:313-331, 2002 17. Shin AY, Morin WD, Gorman JD, et al: The superiority of magnetic resonance imaging in differentiating the cause of hip pain in endurance athletes. Am J Sports Med 2:168-176, 1996 18. Schultz W, Stinus H, Schleicher W, et al: Stress reactions-stress fracture of the upper femoral neck in endurance sports. Sportsverletz Sportschaden 2:81-84, 1991 19. Boden BP, Speer KP: Femoral stress fractures. Clin Sports Med 2:307317, 1997 20. Kaeding CC, Yu JR, Wright R, et al: Management and return to play of stress fractures. Clin J Sport Med 6:442-447, 2005 21. Pihlajamäki HK, Ruohola JP, Kiuru MJ, et al: Displaced femoral neck fatigue fractures in military recruits. J Bone Joint Surg Am 9:19891997, 2006 22. Müller ME: Intertrochanteric osteotomy: indication, preoperative planning, technique in Schatzker, J (ed): The Interochanteric Osteotomy. Berlin, Germany, Springer-Verlag, 1984, pp 25-66 23. Ballmer FT, Ballmer PM, Mast JW, et al: Results of repositioning osteotomies in delayed healing or pseudarthrosis of the proximal femur. Unfallchirurg 10:511-517, 1992 24. Haidukewych GJ, Rothwell WS, Jacofsky DJ, et al: Operative treatment of femoral neck fractures in patients between the ages of fifteen and fifty years. J Bone Joint Surg Am 8:1711-1716, 2004 25. Weistroffer JK, Muldoon MP, Duncan DD, et al: Femoral neck stress fractures: outcome analysis at minimum five year follow-up. J Orthop Trauma 5:334-337, 2003 26. Visuri T, Vara A, Meurman KO: Displaced stress fractures of the femoral neck in young male adults: a report of twelve operative cases. J Trauma 11:1562-1569, 1988 27. Johansson C, Ekenman I, Tornkvist H, et al: Stress fractures of the femoral neck in athletes. The consequence of a delay in diagnosis. Am J Sports Med 5:524-548, 1990
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tress fractures of the femoral neck are being diagnosed with increased frequency as the result of an increased prevalence in the population, increased suspicion on the part of the practitioner, and better imaging modalities. Femoral neck stress fractures have long been a recognized issue with new military recruits,1 and with both an increase in the activity level and in the age of our patients, it has become more common in recreational and elite athletes.2,3 Stress fractures accounts for 50% of new hip pain in military recruits and 10% of new hip pain in recreational athletes. These injuries are seen in 3 distinct patient populations: (1) young, healthy, active individuals such as recreational runners, endurance athletes, or military recruits; (2) individuals with metabolic bone disease from either intrinsic factors such as hormonal
Clinical Associate in Orthopaedics, Massachusetts General Hospital, Boston, MA. Address reprint requests to John B. Sledge III, MD, Sports Medicine North Orthopaedic Surgery, Inc, One Orthopedics Drive, Peabody, MA 01960. E-mail: [email protected]
1060-1872/06/$-see front matter © 2006 Elsevier Inc. All rights reserved. doi:10.1053/j.otsm.2006.10.002
imbalance or extrinsic factors such as steroid use; and (3) elderly who have osteoporosis.4 Stress fractures are part of a diagnostic continuum that has stress fractures on one end and insufficiency fractures on the other. They both have a common final biomechanical pathway in which the repetitive stress on the bone is greater than the bone’s biological ability to sustain the load and/or repair the micro trauma. We will focus our discussion primarily on stress fractures, but most patients will have some degree of both. The level of patient activity usually is the determining variable between the two. New military recruits who develop femoral neck fractures during boot camp are on one end of the spectrum and patients with osteoporosis, hyperparathyroidism, or metabolic bone disease are on the other end. The amenorrheic woman who develops a stress fracture during routine sports has a combination of both. There are grades of patient susceptibility and grades of increased activity. It is the imbalance between the level of activity and the bone’s inherent strength and reparative capabilities that lead to a fracture. Whether it is described as an insufficiency fracture or as a stress fracture depends on whether the activity level or the 265
266 quality of the bone is the major causative fracture. Initial treatment does not differentiate between the 2 causes because surgery and activity modification are treatments for both. Early diagnosis is paramount in the management of both fractures. Fortunately, a delay in the diagnosis and treatment of stress fractures is less common now then it was as a result of an increase in suspicion and better imaging, but when the diagnosis is missed or delayed, there is at best a delay in the patient’s return to activity and at worst a progression to a displaced fracture. Nondisplaced femoral neck stress fractures have a very low rate of avascular necrosis, nonunion, and varus deformity, but these are all risks with displaced fractures. The femoral neck accounts for roughly 50% of all stress fractures, whereas it accounts for only 10% of insufficiency fractures.5 When a stress fracture of the femoral neck is diagnosed, it is important to identify any potential causes of insufficiency and other injury sites.
Risk Factors The most common cause, and therefore the greatest risk factor, is a sudden increase in physical activity, namely running. In a 70-month screening process performed on Finnish military recruits, 85 patients with 92 fatigue injuries were discovered, giving an incidence of 99 per 100,000 personyears.6 In a separate Finnish Military study, 179 recruits were studied at the very beginning of their military service. During the year-long commitment of their service, 15 men experienced stress fractures, with 13 occurring in the first 6 months and 2 occurring in the second 6 months. Tall height, poor physical condition, low hip bone mineral content (BMC), low hip bone mineral density (BMD), and high parathyroid hormone levels were risk factors for stress fractures.7 The lower occurrence in the second 6-month period was attributed to improvements in the recruits’ physical condition, BMC, and BMD, and the fact that those most susceptible to sustaining a fracture had also been selected out by having had one in the first 6 months.7 Exercise is great at increasing bone mass and decreasing the risk for stress fractures, but too much exercise without allowing for bony adaptation is the most common cause of stress fractures. Exercise increases both the bone mass and the bending rigidity of the femoral neck in women between the ages of 18 to 31.8 This increase would theoretically protect women in the same way as it has been shown to protect men.7 The use of oral contraception has been shown to partially mitigate the beneficial effects of exercise.8 There are multiple reports of amenorrheic female athletes being at increased risk for stress fractures in the femoral neck and elsewhere.9,10 Thirty-three military recruits with femoral neck stress fractures had a lower bone mineral density than did 15 patients undergoing treatment for scaphoid nonunions who were used as controls. Although rates of BMD were lower in the stress fracture group, no consistent histomorphometric differences were noted on analysis of the iliac crest, and no patient had osteoporosis.11 When BMD has been used as a screening tool in the initial pool of military recruits, it has not
J.B. Sledge III shown to be a useful predictor; that is to say that people who develop stress fractures have a lower BMD than those who do not, but of the initial recruits that had a low BMD, more did not get fractures than did.7,11,12 Proximal femoral morphology has been thought to play a role in a patient’s susceptibility in developing a stress fracture. The thought has been that a varus neck shaft angle in combination with the hip girdle muscle will increase the tensile forces on the lateral side of the femoral neck and will increase the compressive forces on the medial side. These effects can also be accentuated by an increase in the lateral offset of the proximal femur. Increasing either the varus angle or the lateral offset will increase the torque and/or sheer across the femoral neck. There is some evidence to support this position in that military recruits with coxa vara have a greater incidence and an earlier presentation of stress fractures than the recruits with normal neck shaft angles.7 In a Spanish retrospective assessment, 12 patients with varus femoral necks and stress fractures were paired with 10 patients who had stress fractures and normal neck shaft angles.13 Evaluation showed that patients in the coxa vara group presented at an earlier age, had a longer duration of symptoms and required less of an increase in their activity level to put them at risk.
Presentation and Diagnosis Stress fractures are common overuse injuries seen in athletes and military recruits. The pathogenesis is multifactorial and involves an alteration in the patient’s activity level or in their bone quality. An increase in repetitive submaximal stresses on normal bone is the most common cause, although intrinsic and extrinsic factors such as nutritional status, use of antiinflammatory drugs, radiation, osteoporosis, or hormonal imbalance may contribute to the onset of stress fractures.3 The classic presentation is a patient who experiences the insidious onset of pain after an abrupt increase in the duration or intensity of activity. With femoral neck stress fractures, this often presents with a gradual onset of activity induced anterior hip and thigh pain. Patients often have a hard time localizing the symptoms and can complain of posterior hip pain, lateral hip pain and referred knee pain. Laboratory values are routinely normal. Extensive preactivity blood work in military recruits have not yielded any predictors of stress fractures.7 As mentioned previously, some of the laboratory values were lower in the fracture group then in the control group, but all values were still within the normal range and did not offer any predictive value. An accurate and thorough history in association with sequential radiographs often will suffice to make the diagnosis. This is particularly true when the diagnostic triad are present—a history of recent increase in abnormal repetitive stress, pain increasing with activity and diminishing with rest, and pain in one of the common locations (anterior tibia, metatarsals, calcaneus or femoral neck).14 Bone scan, magnetic resonance imaging (MRI) and occasionally computed tomography (CT) are used for patients presenting with atyp-
Management of femoral neck stress fractures ical exams. Imaging studies are the key to the definitive diagnosis. Plain films often are negative but occasionally will show the classic stress fracture, subperiostial callus, or intraosseous sclerosis. In a series of 60 fractures, plain films showed changes in 39 patients (65%), bone scan was positive in 21 of 24 cases (87%), and CT was positive in 54 of 55 cases (98%).5 Although CT was more accurate than the bone scan at identifying the primary fracture, it was not the imaging modality recommended by the authors because, in this series, when both insufficiency fractures and stress fractures were included, the bone scans identified 31 other noncontiguous fractures. The authors concluded that because radiography signs are inconsistent and because CT can only recognize the primary fracture, that scintigraphy is the imaging modality of choice in patients with a diagnosis of an insufficiency fracture (note: MRI was not used during this study). MRI can detect the early changes of osseous stress injury and can differentiate these from the changes associated with transient osteoporosis. Bone scan alone or more frequently in conjunction with MRI is the recommendation in patients with insufficiency fractures.5 MRI was used to assess the time to resolution of the signal abnormality, with 9 of 10 patients showing resolution of abnormal MR signal intensity on STIR imaging within 6 months of initiating treatment for femoral neck stress fractures.15 Because of the several reports in the literature of MRI documented stress fractures that were not seen with bone scans, the ability of MRI to define the extent of the injury and to be used to assess recovery has made it the imaging modality of choice and scintigraphy has taken a secondary role.14,16 MRI is the modality of choice for differentiating the cause of hip pain in the athlete, including the diagnosis of femoral neck stress fractures. In 19 military recruits with hip pain, bone scan had an accuracy of 68% and a falsepositive rate of 32%.17 The patients then underwent MRI, which was able to differentiate femoral neck stress fractures from muscle injury, tendonitis, avascular necrosis (AVN), unicameral bone cyst, and labral pathology.17,18 MRI has proven to be superior to CT and bone scan in providing early and accurate assessment of the cause of hip pain in young adults.
Classification Stress fractures are classified based on their cause, their location, their severity, their risk of progression, and the appearance of the fracture line. Fractures that are more attributable to excessive repetitive submaximal impact are termed stress fractures, while those more attributable to a decrease in the inherent biomechanical capabilities of the bone are deemed insufficiency fractures. Fractures that occur on the tension side of a bone are aptly called tension fractures, whereas those occurring on the compression side of the bone are appropriately called compression fractures. There was an early attempt to classify stress fractures by their radiographic appearance. This has now been modified to include MRI findings as well.19 Type 1 fractures are MRI-
267 positive fractures, which radiographically may show endosteal or periosteal callus without an overt fracture line. Type 2 fractures radiographic show a nondisplaced fracture line. Type 3 fractures show a displaced fracture line. Some authors have described an MRI finding that they have termed a stress reaction and have hypothesized that this is a precursor to a stress fracture.4 Early in a patient’s course, it is difficult to determine the clinical significance of some MRI findings because of MRI’s sensitivity to marrow changes and the numerous and complex adaptive ways bone can respond to overuse. Fractures have been classified based on their risk of progression or of serious complications. Low-risk fractures are usually those that are type 1 or 2 fractures that are on the compression side of the bone, as they have a low probability for becoming displaced, and a low incidence of serious complication such as pseudoarthrosis, AVN, refracture, progressive arthrosis, or persistent pain. High-risk fractures are just the opposite and are an orthopedic emergency, requiring prompt surgical intervention.1 High-risk tension fracture sites are the femoral neck, the patella, the anterior cortex of the tibia, the medial malleolus, the talus, the tarsal navicular, the fifth metatarsal, and the great toe sesamoids.3,20
Treatment The treatment of femoral neck stress fractures is based on the duration of symptoms, the fracture classification, and the patient’s expectations. One must always look for associated factors, such as metabolic, intrinsic and extrinsic, and treat these contributing variables in conjunction with treating the fracture. If there has been a recent change in the frequency, duration, or intensity of exercise, then activity modification is the initial treatment of low-risk fractures. All stress fractures initially should be treated aggressively because undertreated high-risk fractures can have devastating consequences, but even neglected low-risk femoral neck stress fractures are a challenge to treat, requiring prolonged treatment, extended convalescence, and potentially poor outcome.2 The initial treatment for all stress fractures is activity modification to eliminate all activities causing pain. If the symptoms are only there after sporting or training activities, then only these need to be avoided. If the pain is also present with day-to-day ambulation, then the patient must be made nonweight-bearing. On rare occasions, the symptoms are bilateral, and a wheelchair needs to be used. The return to exercise can parallel the resolution of symptoms and the loss of marrow signal changes on the MRI. When the symptoms have subsided, it is important to put patients through a supervised reconditioning program, as they have just been deconditioned and their tendency is to return back to their previous activity level. A closed-chain activity program has been suggested by many to initially avoid impact loading, with progression to running as the last step. The surgical treatments available are pinning, sliding hip screw, blade plate, and intertrochanteric osteotomy. Although the literature has no comparative studies and the choice often falls to the surgeon’s preference, the reported
268 series do give us some guidance in certain circumstances. First, classify the fracture as discussed previously and look for and start treatment on any identifiable contributing metabolic cause. High-risk fractures and those in elite athletes need to be treated more aggressively then low-risk fractures in recreational athletes. Stress reactions on MRI and low-risk type 1 fractures that do not respond to activity modification may be treated with multiple pins. It is important to use 3 pins that are placed in an inverted triangle with the single inferior screw being placed right along the medial calcar. Low-risk type 2 fractures have the greatest variability and the least consensus on treatment. Small type 2 fractures have been treated successfully with multiple pins. There are reports of successfully treated type 2 fractures with sliding hip screw or blade plate, although these had a higher complication rate then did multiple pins.21 From the selection methods reported, it cannot be determined whether this was the result of implant selection or patient selection. We do not presently use either sliding hip screw or blade plates alone for the treatment of larger low-risk type 2 fractures. Small type 2 fractures with a normal neck angle are treated with multiple pins. Small type 2 fractures with a varus neck or a vertical fracture line and all large type 2 fractures are usually treated with an intertrochanteric osteotomy. There are exceptions such as type 2 fractures with more horizontal fracture lines in recreational athletes who have no pain with ambulation and are willing to give up return to their sport. High-risk type 2 fractures routinely are treated with intertrochanteric osteotomy. My preference is to use the highangle blade plate because it removes less bone, controls rotation, allows for plate assisted reduction techniques, and has better apposition to the lateral side of the femur after the osteotomy. The technique for the osteotomy has been well characterized by both Ballmar and Muller.22,23 Displaced fractures, type 3 fractures, are a surgical emergency and require immediate reduction and internal fixation. Greater than a 24-hour delay has been shown to correlate with a worse prognosis.12 We obtain CT scans on our displaced fractures if there is any question as to fracture pattern, extent or orientation. The outcome of displaced fractures is variable, but a decreased time to reduction and an increased quality of the reduction are consistently correlated with decreased complications (AVN, refracture, pseudoarthrosis and progressive arthrosis) and improved functional outcome.2,12,24,25 If after a reduction is obtained, there is a residual varus alignment or if the fracture line is vertical then consideration should be given to performing an osteotomy at the time of the reduction. The importance of opening the capsule to decompress the hematoma is unclear at this time. With displaced fractures since there is no literature evidence, I will routinely open the capsule anteriorly to help stabilize the head and to assess the quality of the reduction.
Outcome Displaced fractures have a significantly worse prognosis and greater complication rate than nondisplaced fractures and
J.B. Sledge III this has been the topic of most reported series.2 Cannulated screw fixation with fibular graft in patients ages 18 to 50 with displaced femoral neck fractures showed only a 90.6% fusion rate and even these showed a decreased Harris Hip score of only 87.1.2 In another study, 42 patients with displaces fractures were treated with either a compression hip screw (17 cases) or multiple cancellous screws (25 cases). Ten patients developed AVN at average follow-up of 5.6 years. Risk factors identified for the development of AVN were delay in reduction and fixation (1.5 days versus 5.9 days), postoperative varus alignment, and the use of screws.12 Of the 42 patients 71% had good-to-excellent results, 9.5% had acceptable results, and 19% had poor results. Eight patients required prosthetic replacements. In 12 surgically treated displaced femoral neck fractures in young male military recruits, AVN developed in 5. These patients were treated early with a sliding hip screw in 10 cases and either a Jewett nail or an OA 130° blade plate in the other 2. Nonunion developed in 3 cases, 2 of whom later went on to develop AVN. Only 6 patients (50%) were scored as good or excellent at follow-up.26 A series of 25 patients who were treated nonoperatively were contacted retrospectively 5 to 7 years after their diagnosis.25 No patient had developed AVN, nonunion, valgus deformity, or posttraumatic arthritis. On self-administered outcome measures, 68% of patients felt “somewhat bothered” in at least one functional category on the Musculoskeletal Function Assessment, and 9 patients (36%) felt “disabled.” There was no correlation between fracture location (tension of compression), treatment method, or BMD. This series demonstrates that even in patients whose diagnosis was timely, their treatment appropriate and no major complications, that the long-term outcome for these patients is often not a return to normal function. A report of college athletes and runners showed that with nondisplaced, low-risk, compression type femoral neck fractures with early diagnosis and treatment with nonweightbearing activity followed by activity modification, there was excellent healing.19 The patients were separated into 2 groups: recreational athletes and elite athletes. There was a significant difference in ability to return to sports in that none of the elite athletes were able to return to their previous level of performance. In 23 patients followed up at an average of 6.5 years after their diagnosis, the patients’ outcome correlated with fracture type and duration of symptoms.27 Seven patients with type 1 fractures (positive MRI, but no fracture line on plain film) that were diagnosed with less than 6 months of symptoms were all treated with activity modifications. All but 1 healed without incident, whereas 1 progressed and required surgical intervention. Of the remaining 16 patients treated surgically, 6 required repeat operations. Of the 6, 5 had type 3 fractures (displaced) and 1 had a type 2 fracture (nondisplaced visible fracture). Reoperation was required for AVN in 3, pseudoarthrosis in 2, and refracture in 1. At follow-up, the overall results were good to excellent in 14 and bad or fair in 9. When tension side fractures were removed from the analysis, there was a trend toward more severe fractures, as measured
Management of femoral neck stress fractures by fracture type, as the duration of the patient’s symptoms increased.27
Summary Stress fractures are being diagnosed more frequently as the resulf of our increased suspicion and their increasing prevalence. The history and physical examination will usually place stress fractures on the differential diagnosis, and the situation is further clarified by an assessment of the potential intrinsic and extrinsic contributing factors. Plain radiographs will often confirm the diagnosis, but if not further imaging will be required. If an insufficiency fracture is suspected then MRI and bone scan should be considered, but if a stress fracture is more likely then just MRI will suffice. If the fracture is displaced I prefer a CT instead of the MRI. With imaging, the fracture can be classified and, in conjunction with the patient’s expectations, an appropriate treatment course can be selected. Improved outcomes largely depend on shorter duration of symptoms, shorter times to diagnosis, low-risk fractures, lesser fracture type and appropriate treatment. When surgery is performed the goals are rapid identification of the fracture, early anatomic reduction, removal of varus neck angle and placement of the fracture line in as horizontal an orientation as reasonable. Mild fractures in the recreational athlete will lead to a period of decreased activity, rapid healing, and return to full activity. More severe fractures will require more intervention and a significantly longer interruption in their activities. It is crucial that the treating physician focus on the long term outcome and inform the patient that this will require 6 to 18 months of treatment before full activity can be reinitiated. It is unlikely that elite or professional athletes or those with highrisk fractures will be able to return to their careers.
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