Journal Logo

Supplement Article

Hot Topics in Biomechanics

Hip Fracture Fixation

Olson, Steven A. MD*; Schemitsch, Geoffrey; Morwood, Michael MD*; Schemitsch, Emil MD, FRCSC†,‡; Russell, Thomas A. MD§; Latta, Loren L. PhD, PE

Author Information
Journal of Orthopaedic Trauma: December 2015 - Volume 29 - Issue - p S1-S5
doi: 10.1097/BOT.0000000000000471

Abstract

INTRODUCTION

An estimated 34,000 hip fractures occurred in patients in the United States in 1996,1 and approximately 1.7 million hip fractures worldwide occurred that year. Between 1986 and 2005, the annual mean number of hip fractures was approximately 950 per 100,000 for women and 400 per 100,000 for men.1 As life expectancy increases, the number of patients over the age of 65 will continue to grow, and thus, it is expected that the burden of disease for geriatric hip fractures will substantially increase over time.2 Most intertrochanteric hip fractures are treated with reduction and surgical fixation. In general, the types of fixation can be broken down into intramedullary (IM) and extramedullary,2,32,3 with extramedullary fixation consisting largely of plate and screw constructs for the proximal femur. This article will review varying types of IM and extramedullary fixation, evaluate existing biomechanical models, and discuss the application of fracture models to clinical practice.

IM NAILING OF PROXIMAL FEMUR FRACTURES

Proximal femur fractures have traditionally been treated with the use of either an IM nail or an extramedullary sliding hip screw (SHS). Because of the devastating nature of proximal femur fractures, the efficacy of the differing treatment options must be assessed, especially when treating unstable fractures or when signs of comminution, osteoporotic bone, or pathologic bone are present. Treatment has trended toward the use of IM nails versus plating and SHSs. A study by Anglen and Weinstein4 examined the relative use of plates or nails during fixation of intertrochanteric femur fractures from 1999 to 2006. The results indicated an increase in the use of nails during fixation from 3% to 67% and a subsequent decline in the use of plates from 97% to 33%.4

This rise in nailing can be attributed to a number of factors, including certain biomechanical advantages when compared with SHSs, especially during fixation of unstable fractures like transtrochanteric, reverse oblique, or subtrochanteric extension fractures. These biomechanical advantages may translate into patient-important outcomes, such as reduced reoperation rates. For example, a study by Matre et al5 examining 2716 intertrochanteric fractures found that patients who were treated with SHSs had a 43% higher risk of reoperation. Furthermore, IM nailing was favored when patient pain, satisfaction, quality of life, and mobility were examined. A study by Sadowski et al6 examined the treatment of 39 unstable proximal femur fractures with either an IM nail or a 95 degree screw-plate in elderly patients. Implant failure was observed in 7 of the 19 patients who were treated with the screw-plates compared with 1 of 20 in the group treated with IM nails. Shorter hospital stays were also observed in a study by Bohl et al,7 which examined the use of either IM nailing or an extramedullary implant on 4432 patients with intertrochanteric femur fractures. This decreased hospital stay may offset the higher cost of an IM nail. Swart et al8 furthermore elucidated the cost-effectiveness of IM nailing in unstable proximal fractures when accounting for the hardware failure rate.

Modern nails are advantageous in that they are smaller, have high cutout resistance, excellent lag screw stability, and dynamization capability. The following are recommendations to maximize the effectiveness of IM nailing in proximal femur fixation. First, the correct entry point must be obtained and proper reduction achieved before reaming. The implant construct should be optimized. With simple, well-reduced fractures, the choice of implant is not critical. With unstable fractures, the implant that allows minimal fracture site motion should be used.9The lag screw should be placed in a center/center position or center/inferior position in the head with static locking,10,1110,11 and the length of the nail does not seem to make a difference.12

FIXATION RECOMMENDATIONS—PLATING

The initial forms of internal fixation for geriatric hip fractures consisted of fixation constructs using plates with fixed angle nails or blades in the proximal femur.13 These techniques gradually transitioned to the use of an SHS. In 1964, Clawson13 described the treatment of intertrochanteric hip fractures with an SHS fixation method. In this work, he reported that “stable” fracture patterns did well with fixed angle nail-plate devices, but that unstable fractures continued to have problems. An improved fixation has been demonstrated with sliding hip devices when compared with traditional fixed angle implants.13,1413,14 Valgus alignment of the initial reduction of intertrochanteric hip fractures has been shown to be beneficial, as intertrochanteric fractures often tend to collapse into a stable position with healing, and the SHS therefore allows for a controlled collapse of the fracture, maintaining length and a functional abductor mechanism after healing.3,133,13

Baumgaertner et al14 described the importance of the compression screw position to the overall stability of intertrochanteric hip fractures, indicating that the screw needs to be placed in a center–center position on both the AP and lateral views and quite deep in the femoral head. Haidukewych et al15 reported that reverse obliquity intertrochanteric fractures have a much more successful rate of union and lower loss of reduction with IM fixation as compared with plate fixation. More recently, Palm et al16 identified that the integrity of the lateral wall of the proximal femur is important in identifying potential failure with an SHS. Specifically, lack of continuity of the proximal lateral wall of the femoral shaft was found to allow the proximal fragment to collapse excessively laterally, leading to substantial shortening of the abductor mechanism. The lateral wall effect can be counteracted with a trochanteric buttress plate or stabilization plate to prevent excess collapse.15,1715,17 However, this technique has been found to be, at best, equivalent to or slightly less effective than IM fixation.

The primary factors under the control of the surgeon treating patients with intertrochanteric hip fractures are the quality of the reduction obtained during surgery and the placement of the implants. Often, closed reduction techniques are used to reposition the proximal femoral fragment relative to the shaft. However, there are times when, because of comminution or significant soft tissue tensions, the alignment of the fragments may not be ideal to allow for stable compression leading to well-positioned fracture healing. In these cases there may be need for adjunctive open reduction at the time of internal fixation. Several authors have described the benefit of performing a manual assessment of the fracture alignment of the anterior cortex of the femoral shaft with the anterior portion of the intertrochanteric fragment ensuring that there is bony contact and stability at the time of fixation.18–2018–2018–20 Furthermore, care must be taken at the time of implanting the fixation device to not alter the alignment of the fracture fragments and to prevent rotational or angular displacement. Sommers et al used a laboratory model to simulate the clinically-seen failure mechanism of screw cutout from the proximal head and neck portion of the intertrochanteric fracture fragment.21 In this work, the authors observed that rotational displacement of the proximal fragment, specifically into varus and extension as observed clinically, was responsible for the cutout failures seen in biomechanical tests. Because this observation, the importance of rotational stability of the fracture fragment has been emphasized. Varying derotational devices consisting of screws and side plates have therefore been introduced to provide a more stable rotational environment for the intertrochanteric fragment.3,22,233,22,233,22,23

The results of several prospective, randomized trials that compare plate fixation to nailing are shown in Supplemental Digital Content 1 (see Table, http://links.lww.com/BOT/A554).22–2622–2622–2622–2622–26 Generally, these data demonstrate little to no difference in terms of overall complications and the medical aspects of care. Overall, healing rates are similar between IM and plate-based constructs in studies that consider 31-A1 and 31-A2 fractures.18 An improvement was observed in healing with maintenance of the reduced position for IM fixation, particularly for the more unstable fracture patterns.

The results of studies that assess different types of plate fixation for geriatric intertrochanteric fractures have been compiled in Supplemental Digital Content 1 (see Table, http://links.lww.com/BOT/A555).19,20,2719,20,2719,20,27 The percutaneous compression plate (PCCP) and the compression hip screw have been shown to have similar rates of overall complications, but the PCCP exhibited evidence for an improved maintenance of the reduction position.

A recent Cochrane review compared different plate fixation methods for intertrochanteric femur fractures. Fixed angle plates, including the Jewett fixed nail type and the Resistance Augmented Bateaux plate, were compared with SHSs, PCCPs, and other devices.3 The authors concluded that fixed nail plates had a greater fixation failure rate when compared with SHSs, and thus, SHSs continue to be the overall preference for intertrochanteric fracture fixation.

Plate fixation remains an important type of implant for stable intertrochanteric hip fractures. Importantly, the cost of an SHS is substantially less than the cost of an IM device for fixation of the same fracture.28 Indeed, studies with devices such as the PCCP and other rotationally stable plating systems may show an improved overall final position at the time of fracture healing. However, data demonstrating that these rotationally stable implants also improve quality of life and reduce revision rates is lacking, and thus, they may not warrant the added costs associated with their use. Proactively managing costs and quality of care is of increasing importance,2 as surgeons must consider both the quality and value of the care they deliver. Better data are therefore needed to inform orthopaedic surgeons as to what treatment options result in both improved quality and increased overall value for patients.

SELECTING THE BEST MODEL: COMPARING EXISTING DEVICES TO NEW CONSTRUCTS

Two fragment OTA 31-A1, 2, and 3 type fractures are inherently stable once reduced and fixed. OTA 31-A2.1, 2, and 3 fractures, all having more than 2 fragments, are difficult to reduce, often have a compromised medial buttress, and are inherently unstable. Most fracture models aim to address A2 type fractures, because they result in the most biomechanical failures clinically. The most common mechanical failure modes for fixed nail-plate devices include head cutout, varus angulation, screw loosening or pull out, and nail-plate junction failure. Failure modes for sliding nail-plate devices include excessive collapse, varus angulation, screw loosening, and less often head cutout if the sliding mechanism jams. IM devices also can have head cutout if the sliding mechanism of the head and neck screws jam in the nail. Excessive collapse, varus angulation, and fracture of the femoral shaft in the subtrochanteric region can occur at the distal cross screw.

These failure modes can be duplicated with a single compression load on the proximal femur in cadaver bones with 3 or 4 part OTA 31-A2.1-3 type fracture patterns. Fresh frozen human femurs make the best model, and formalin fixed femurs have been used successfully. Some synthetic bone models may work well but must be validated.

Most models try to simulate the compression load at heel strike, which is typically the peak load seen during activities of daily living. With most fracture models, the expected clinical failure modes can be duplicated with this simple loading. For other loading conditions one can visit Orthoload.com to see the magnitude and direction of loads on the hip for a wide variety of activities. Regardless of the magnitude and alignment of the chosen load, the end conditions for the bone-fracture-fixation construct are critical to properly simulate the behavior seen clinically. The femoral head must be able to rotate in any direction as it would in the acetabulum. Varus rotation is the most common rotation seen clinically. Most testing machines can apply an axial compression load in the vertical direction, so the distal femur must be aligned to vertical at the angle of the desired applied load. The proximal or distal boundary condition must either allow both fragments to rotate as load is applied (Fig. 1A), or if one is held in a fixed angle to vertical, it must be allowed to translate (Fig. 1B).29,3029,30 Both of these models work well, as they allow the fractured fragments to rotate relative to each other as would occur in a live subject.

FIGURE 1
FIGURE 1:
A, The femoral shaft is aligned to the vertical load to simulate the expected angle of the peak load on the hip joint during ambulation. The distal fragment must be able to translate for the bone fragments to angulate naturally.29 B, The femoral shaft is aligned to the vertical load to simulate a load along the mechanical axis of the femur. The distal femur must be allowed to rotate for the bone fragments to angulate naturally.30

If the objective is to simulate a sudden type of mechanical failure, a single load can be applied to the model until failure is observed. If loosening or fatigue is the desired failure mode, cyclic loading can be applied. A single direction of load at a single point aligned to the femoral head is often quite effective. Adding an abductor load creates a more realistic moment at the hip joint but is often impractical with intertrochanteric fractures because the abductor load must be applied to the greater trochanter, which can be very weak and may not tolerate the load. With robotic load application one can achieve very complex loading cycles to simulate a variety of activities. For instance, in rare cases the sliding screw has pulled out of the barrel of the nail plate. This type of failure cannot occur with the simple loading described above, but certain activities, such as getting in or out of bed, have shown a reversing component of the load on the femoral head that might tend to pull the screw from the barrel (see Orthoload.com).

The other issue important to fracture fixation is the quality of bone. Mechanical failures are much more prevalent in osteoporotic bone than in normal bone in young, healthy subjects. Unfortunately, most of these very unstable fractures occur in the more elderly population, in which osteoporosis is more prevalent. Most of these unstable fracture models have shown that if the medial cortex can be aligned at the time of fixation, the fracture will behave in a stable manner.31,3231,32 However, the fixation must be sound enough to keep the bone fragments reduced. Cancellous bone in the femoral head is strong enough to accomplish this in normal bone, but in an osteoporotic femoral head and neck it is much sparser, unevenly distributed, and usually absent in the very location where most screws tend to end up after surgical fixation. It is therefore very difficult to prevent slip of the medial cortex of the proximal fragment off the medial cortex of the distal fragment, which results in the proximal fragment rotating into varus. This common occurrence can be modeled well with osteoporotic human femurs but not with current synthetic femur models.

The development of an appropriate biomechanical model begins with careful definition of the clinical problem to be addressed, followed by appropriate choice of materials, boundary conditions, and loading conditions to mimic the clinical situation. One must then validate the model before planning the definitive study sample size and outcome measures.

TRANSLATING BIOMECHANICAL STUDIES INTO CLINICAL PRACTICE

Bones have the unique ability to repair structural failure with the resorption and creation of new bone into a structurally equivalent functional construct. Conversely, human biomaterials do not yet possess self-regeneration abilities, and thus, bone regeneration in the fracture zone is the only hope for survival of the implant. Anything man-made will fail in an unstable fracture or bone defect environment; it is only an issue of how, when, and why. Biomechanical studies to determine the modes and time to failure of implants have been developed in an attempt to forecast survival rates in hip implants. The Smith-Petersen Nail designed in 1925 and combined with an open anatomic reduction was the first globally successful device for hip fracture fixation. With widespread use of this technique and device, new failure modes were discovered, including electrogalvanic corrosion.33,3433,34 Smith35 in 1953 first reported mechanical testing involving the creation of femoral neck fractures and the loads to create fractures. Building on this information, Martz and Foster pioneered the load to failure model for hip fracture testing, estimating the loads required for a hip fracture implant to fail.36,3736,37 Unfortunately, this focus on implant survivability diverted attention away from surgical reduction and the functional recovery of the patient.

In 1963, the theoretical modeling of fracture implant stability took a wrong turn when Holt suggested that rotational forces were unimportant in pertrochanteric fractures, and this single article resulted in 40 years of stasis in hip fracture biomechanical modeling.38 In 2004, Sommers et al developed a new biomechanical model for hip fracture stability, demonstrating the importance of rotation in hip screw cutout, the most important mode of failure for hip fracture fixation.21

Ehmke et al39 renewed the appreciation of multiplanar loading vectors on hip fracture fixation and implant migration, as proposed by Smith-Petersen 80 years earlier. This article helped stimulate investigation of another form of implant failure affecting patient functional outcome: that of fracture collapse and shortening of the hip. This complication was largely ignored as a sacrifice to prevent implant failure. In 2008, Zlowodski et al40 demonstrated in a multicenter study the negative effect of excessive shortening of the hip.

Another aspect of hip fracture modeling is the quality of the patient's bone. Insufficient bone quality is one aspect of fracture repair that often justified arthroplasty replacement surgery. New calcium phosphate cements with intrusion properties combined with augmented implant designs present the potential to modify the material properties of the next generation of hip implants.41

New biomechanical models will continue to be required to reflect clinically relevant issues and to optimize the current generation of hip fixation systems. The ultimate goal should be the ability for a hip fracture patient to expect the same functional recovery as elective total hip arthroplasty patients.

REFERENCES

1. Brauer CA, Coca-Perraillon M, Cutler DM, et al.. Incidence and mortality of hip fractures in the united states. JAMA. 2009;302:1573–1579.
2. American Academy of Orthopaedic Surgeons, Management of Hip Fractures in the Elderly: Evidence-Based Clinical Practice Guideline. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2014.
3. Parker MJ, Das A. Extramedullary fixation implants and external fixators for extracapsular hip fractures in adults. Cochrane Database Syst Rev. 2013. doi: 10.1002/14651858.CD000339.pub3.
4. Anglen JO, Weinstein JN; Committee ABoOSR. Nail or plate fixation of intertrochanteric hip fractures: changing pattern of practice. J Bone Joint Surg Am. 2008;90:700–707.
5. Matre K, Havelin LI, Gjertsen JE, et al.. Sliding hip screw versus im nail in reverse oblique trochanteric and subtrochanteric fractures. A study of 2716 patients in the norwegian hip fracture register. Injury. 2013;44:735–742.
6. Sadowski C, Lübbeke A, Saudan M, et al.. Treatment of reverse oblique and transverse intertrochanteric fractures with use of an intramedullary nail or a 95 screw-plate. J Bone Joint Surg Am. 2002;84:372–381.
7. Bohl DD, Basques BA, Golinvaux NS, et al.. Extramedullary compared with intramedullary implants for intertrochanteric hip fractures. J Bone Joint Surg Am. 2014;96:1871–1877.
8. Swart E, Makhni EC, Macaulay W, et al.. Cost-effectiveness analysis of fixation options for intertrochanteric hip fractures. J Bone Joint Surg Am. 2014;96:1612–1620.
9. Roberts CS, Nawab A, Wang M, et al.. Second generation intramedullary nailing of subtrochanteric femur fractures: a biomechanical study of fracture site motion. J Orthop Trauma. 2002;16:231–238.
10. Kuzyk PR, Shah S, Zdero R, et al.. A biomechanical comparison of static versus dynamic lag screw modes for cephalomedullary nails used to fix unstable peritrochanteric fractures. J Trauma Acute Care Surg. 2012;72:E65–E70.
11. Kuzyk PR, Zdero R, Shah S, et al.. Femoral head lag screw position for cephalomedullary nails: a biomechanical analysis. J Orthop Trauma. 2012;26:414–421.
12. Okcu G, Ozkayin N, Okta C, et al.. Which implant is better for treating reverse obliquity fractures of the proximal femur: a standard or long nail? Clin Orthop Relat Res. 2013;471:2768–2775.
13. Clawson DK. Trochanteric fractures treated by the sliding screw plate fixation method. J Trauma. 1964;4:737–752.
14. Baumgaertner MR, Curtin SL, Lindskog DM, et al.. The value of the tip-apex distance in predicting failure of fixation of peritrochanteric fractures of the hip. J Bone Joint Surg Am. 1995;77:1058–1064.
15. Haidukewych GJ, Israel TA, Berry DJ. Reverse obliquity fractures of the intertrochanteric region of the femur. J Bone Joint Surg Am. 2001;83:643–650.
16. Palm H, Jacobsen S, Sonne-Holm S, et al.. Integrity of the lateral femoral wall in intertrochanteric hip fractures: an important predictor of a reoperation. J Bone Joint Surg Am. 2007;89:470–475.
17. Templeman D, Baumgaertner MR, Leighton RK, et al.. Reducing complications in the surgical treatment of intertrochanteric fractures. Instr Course Lect. 2005;54:409–415.
18. Marsh J. Ota fracture classification. J Orthop Trauma. 2009;23:551.
19. Baird RP, O'Brien P, Cruickshank D. Comparison of stable and unstable pertrochanteric femur fractures managed with 2-and 4-hole side plates. Can J Surg. 2014;57:327.
20. Peyser A, Weil Y, Brocke L, et al.. A prospective, randomised study comparing the percutaneous compression plate and the compression hip screw for the treatment of intertrochanteric fractures of the hip. J Bone Joint Surg Br. 2007;89:1210–1217.
21. Sommers MB, Roth C, Hall H, et al.. A laboratory model to evaluate cutout resistance of implants for pertrochanteric fracture fixation. J Orthop Trauma. 2004;18:361–368.
22. Knobe M, Drescher W, Heussen N, et al.. Is helical blade nailing superior to locked minimally invasive plating in unstable pertrochanteric fractures? Clin Orthop Relat Res. 2012;470:2302–2312.
23. Guo Q, Shen Y, Zong Z, et al.. Percutaneous compression plate versus proximal femoral nail anti-rotation in treating elderly patients with intertrochanteric fractures: a prospective randomized study. J Orthop Sci. 2013;18:977–986.
24. Adams C, Robinson C, Court-Brown CM, et al.. prospective randomized controlled trial of an intramedullary nail versus dynamic screw and plate for intertrochanteric fractures of the femur. J Orthop Trauma. 2001;15:394–400.
25. Ahrengart L, Törnkvist H, Fornander P, et al.. A randomized study of the compression hip screw and gamma nail in 426 fractures. Clin Orthop Related Res. 2002;401:209–222.
26. Haq RU, Manhas V, Pankaj A, et al.. Proximal femoral nails compared with reverse distal femoral locking plates in intertrochanteric fractures with a compromised lateral wall; a randomised controlled trial. Int Orthop. 2014;38:1443–1449.
27. Fitzpatrick DC, Sheerin DV, Wolf BR, et al.. A randomized, prospective study comparing intertrochanteric hip fracture fixation with the dynamic hip screw and the dynamic helical hip system in a community practice. Iowa Orthop J. 2011;31:166.
28. Torio CM, Andrews RM. National Inpatient hospital costs: The Most Expensive Conditions by Payer. Healthcare Cost and Utilization Project (HCUP) Statistical Briefs [Internet]. Rockville, MD: Agency for Health Care Policy and Research; 2006-2013.
29. Hoffmann S, Paetzold R, Stephan D, et al.. Biomechanical evaluation of interlocking lag screw design in intramedullary nailing of unstable pertrochanteric fractures. J Orthop Trauma. 2013;27:483–490.
30. McConnell A, Zdero R, Syed K, et al.. The biomechanics of ipsilateral intertrochanteric and femoral shaft fractures: a comparison of 5 fracture fixation techniques. J Orthop Trauma. 2008;22:517–524.
31. Yoshimine F, Latta LL, Milne EL. Sliding characteristics of compression hip screws in the intertrochanteric fracture: a clinical study. J Orthop Trauma. 1993;7:348–353.
32. Latta L, Tronzo R, Amaya W, et al.. Comparative intertrochanteric fracture fixation in osteoporotic and normal femora. J Orthop Trauma. 1988;2:61–62.
33. Venable C, Stuck WG. Results of recent studies and experiments concerning metals used in the internal fixation of fractures. J Bone Joint Surg Am. 1948;30:247–250.
34. Scales JT, Winter G, Shirley H. Corrosion of orthopaedic implants. BMJ. 1961;2:478.
35. Smith L. Hip fractures: the role of muscle contraction or intrinsic forces in the causation of fractures of the femoral neck. J Bone Joint Surg Am. 1953;35:367–383.
36. Martz CD. Stress tolerance of bone and metal. J Bone Joint Surg Am. 1956;38:827–834.
37. Foster J. Trochanteric fractures of the femur treated by the vitallium mclaughlin nail and plate. J Bone Joint Surg Br. 1958;40:684–693.
38. Holt EP. Hip fractures in the trochanteric region: treatment with a strong nail and early weight-bearing. J Bone Joint Surg Am. 1963;45:687.
39. Ehmke LW, Fitzpatrick DC, Krieg JC, et al.. Lag screws for hip fracture fixation: evaluation of migration resistance under simulated walking. J Orthop Res. 2005;23:1329–1335.
40. Zlowodzki M, Brink O, Switzer J, et al.. The effect of shortening and varus collapse of the femoral neck on function after fixation of intracapsular fracture of the hip: a multi-centre cohort study. J Bone Joint Surg Br. 2008;90:1487–1494.
41. Russell TAT, Browne TD, Jacofsky M, et al.. The problem of fracture fixation augmentation and description of a novel technique and implant for femoral neck stabilization. Tech Orthop. 2015;30:22–27.
Keywords:

bone fractures; hip fractures; fracture fixation; Biomechanics

Supplemental Digital Content

Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.