Evaluation of the osteoporotic proximal humeral fracture and strategies for structural augmentation during surgical treatment

J Shoulder Elbow Surg (2012) 21, 1787-1795

www.elsevier.com/locate/ymse

REVIEW ARTICLES

Evaluation of the osteoporotic proximal humeral fracture and strategies for structural augmentation during surgical treatment Surena Namdari, MD, MSc, Pramod B. Voleti, MD, Samir Mehta, MD* Department of Orthopaedic Surgery, Hospital of the University of Pennsylvania, Philadelphia, PA, USA Fractures of the proximal humerus are relatively common injuries in the elderly population. Given the association between proximal humeral fractures and osteoporosis, elderly patients who sustain these injuries should always undergo a fragility fracture workup. Furthermore, a preoperative assessment of local bone quality can be critical in facilitating decision making regarding surgical and nonsurgical treatment. Modalities for quantifying osteoporosis in the proximal humerus include plain radiography and spiral computed tomography imaging. Optimal management of osteoporotic proximal humeral fractures has evolved and may now includes use of locking plates and augmentation with intramedullary fibular grafts, calcium phosphate or sulfate cement, and iliac crest bone graft. This article reviews the demographics of patients who sustain proximal humerus fractures, the appropriate postinjury fragility fracture workup, modalities for quantifying osteoporosis in the proximal humerus, techniques for augmenting fixation of proximal humerus fractures, and the authors’ preferred approach to the treatment of these injuries. Level of evidence: Review Article. Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Osteoporosis; proximal humerus fracture; bone mineral density; augmentation

Demographics Fractures of the proximal humerus are relatively common injuries, accounting for 5% of all fractures,9,17,25 with an incidence of approximately 66/10,000 person-years.27 The incidence increases rapidly with age, with the highest age-specific incidence occurring in women aged 80 to 89 years.10 In fact, more than 70% of proximal humeral fractures occur in patients aged older than 60 years.56,57 The male-to-female ratio for proximal humeral fractures Investigational Review Board approval was not required for this review article. *Reprint requests: Samir Mehta, MD, Department of Orthopaedic Surgery, Hospital of the University of Pennsylvania, 3400 Spruce St, 2 Silverstein, Philadelphia, PA 19104, USA. E-mail address: [email protected] (S. Mehta).

has been estimated at 3:7.10 When looking only at patients aged between 30 and 60 years, the incidence of these fractures is equal between men and women.48 However, although the incidence increases in both men and women after age 50 years, the incidence in women increases by a 4:1 ratio.48 The age and sex distribution of proximal humerus fractures underscores the role of osteoporosis in these injuries.

Osteoporosis The risk factors for proximal humeral fractures are primarily associated with low bone mineral density (BMD) and an increased risk of falls.9,29,48 The mechanism of injury for proximal humeral fractures in young patients is often related to high-energy trauma; however, the most

1058-2746/$ - see front matter Ó 2012 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2012.04.003

1788 common mechanism in elderly patients is a fall from standing height onto an outstretched upper extremity.10 The distribution of mechanisms of injury for proximal humerus fractures in one series was falls from standing height, 87%; falls from significant height, 4%; motor vehicle collisions, 4%; athletics, 4%; and a direct blow, 1%.10 Osteoporosis is the most common metabolic bone disease in the Western world and is recognized as a major cause of disability and morbidity in older men and women.20,32 It has been described as a silent epidemic that manifests clinically as fragility fractures predominantly of the distal radius, proximal femur, spine, and proximal humerus.12 Although research and treatment of fragility fractures have commonly focused on proximal femoral fractures, upper extremity fractures account for one-third of the total incidence of fractures in the elderly.29,40,52 Upper extremity fractures can considerably limit independence in an elderly individual and may lead to a permanent move to a nursing home in 6% of patients.32 They also demand considerable resources, which may include operative intervention and in-patient rehabilitation.32 The incidence of proximal humeral fractures significantly increases in osteoporotic bone.9,29,48 A study of women with a high risk of fall found the incidence of proximal humeral fractures was 2.6 times greater in osteoporotic (12.1/1,000 woman-years) than nonosteoporotic (4.6/1,000 woman-years) women.29 Furthermore, low-energy osteoporotic fractures of the proximal humerus have shown a 3-fold increase in incidence during the last 3 decades.21,44 As a result of the anticipated aging population, an additional 3-fold increase is expected in the next 30 years.21 In addition to increasing the risk of proximal humeral fractures, osteoporosis increases the difficulty of managing these injuries. This is primarily because higher BMD is important for the stability of fixation.34 BMD is highly correlated with pullout strength of screws51 and has a major effect on the biomechanical behavior of the bone-to-implant construct.13

Fragility fracture workup A low-energy proximal humeral fracture in an elderly patient is an indicator of underlying osteoporosis. Previous series have shown that proximal humeral fractures more reliably correlate with bone fragility than do fractures of the spine, proximal femur, pelvis, or distal radius.41 Another investigation showed that proximal humeral fractures are independent predictors of subsequent hip fractures: an individual who has sustained a proximal humeral fracture is 5 times more likely to have a hip fracture within 1 year after injury.8 Given the association between proximal humeral fractures and osteoporosis, elderly patients who sustain fractures of the proximal humerus should undergo a fragility fracture workup. The important elements of the fragility fracture work-up are briefly highlighted below.

S. Namdari et al.

Skeletal history and risk factor assessment A careful skeletal history should be obtained and documented in all patients with fragility fractures. The complete skeletal history includes a survey of previous fractures, corresponding mechanisms of injury, and complications of fracture healing. A thorough risk assessment, which includes evaluation of personal risk factors, medical conditions, and medications, should also be completed.

Physical examination, laboratory evaluation, and BMD testing The physical examination for all patients with fragility fractures should focus on detecting occult sequelae of osteoporosis, secondary medical causes of bone loss, and signs of increased risk of fall. The initial laboratory evaluation may include serum electrolytes, liver and kidney function tests, albumin, total protein, calcium, intact parathyroid hormone, 25-hydroxy vitamin D, phosphorus, magnesium, thyroidstimulating hormone, serum testosterone, and a complete blood count. These studies may be tailored for patients by findings in the history and physical examination to avoid unnecessary testing. At our institution, a consultation with geriatrics is routinely completed, and an outpatient prescription for a dual-energy X-ray absorptiometry (DXA) scan is provided if one has not been done in the past 12 months.

Treatment and prevention The treatment and prevention of osteoporosis as the cause of fragility fractures entails a multifactorial approach, which includes alteration of modifiable personal risk factors, management of secondary medical causes of bone loss, elimination of medications that contribute to bone loss, reduction of fall and injury risk, and initiation of pharmacologic and nonpharmacologic interventions that increase bone mass. The pharmacologic management of fragility fractures is controversial. The initial treatment at our center after fracture includes supplementation with vitamin D and calcium, nutritional counseling, and cessation of bisphosphonate use. Osteoblastic agents are not typically prescribed in the acute postoperative period.

Quantifying osteoporosis in the proximal humerus Failure after internal fixation of osteoporotic fractures of the proximal humerus due to loss of reduction and varus collapse are often observed even with the use of locking plates.19,43,46,54 Accordingly, the preoperative assessment of local bone quality can be important in facilitating decision making regarding surgical and nonsurgical treatment of patients sustaining these injuries. Any method to assess

Osteoporotic proximal humeral fractures

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bone quality of the proximal humerus after a fracture should be technically easy, reproducible, and cost-effective.

Plain radiography The cortical thickness of various bone sites such as the femur, radius, metacarpals, and humerus is an effective predictor in assessing osteoporotic changes in bone.4,37,38,59 In 1980, Bloom et al4 used the combined cortical thickness at a point approximately 10 to 12 cm proximal to the most distal end of the humerus as an index of osteoporosis in women. Tingart et al58 expanded on this concept in a cadaveric study that used DXA to correlate the BMD of the proximal humerus with the cortical thickness of the proximal humeral diaphysis as measured on anteroposterior radiographs. The cortical thickness is measured at (1) the most proximal level of the humeral diaphysis where the endosteal borders of the lateral and medial cortices are parallel to each other and (2) 20 mm distal to level 1 (Fig. 1). The combined cortical thickness is calculated as a mean of the medial and lateral cortical thicknesses at the 2 levels and adjusted for the magnification factor of the radiograph. Tingart et al58 determined that specimens with a combined cortical thickness of less than 4 mm had a significantly lower BMD of the humeral head, surgical neck, and greater and lesser tuberosities than those with a cortical thickness of greater than 4 mm. Subsequently, they hypothesized that internal fixation of fractures of the proximal humerus in patients with combined cortical thickness of less than 4 mm may be complicated by loosening/failure of the implant. Using linear regression, their study provides equations61 that can be used to predict the BMD (g/cm2) for each region of the proximal humerus from mean cortical thickness measurements (Table I). Hepp et al18 determined cortical index in 113 consecutive patients with displaced proximal humerus fractures status after a fall onto the shoulder.4 They compared this cohort with a comparative matched-group of patients with a fall on the shoulder without a fracture.4,18 They calculated the total area at the region of the humerus described by Bloom et al4 and defined cortical index as (total area
marrow area)/(total area). They noted that the cortical index was significantly lower in the fracture group (0.28 vs 0.47, P < .01). Patients in the fracture group underwent internal fixation with a locked plate. They were unable to correlate cortical index measurements with need for reoperation (P ¼ .085), although they may have been underpowered to conduct this analysis. Methods for predicting proximal humerus BMD via radiographs provide the most cost-effective and technically uncomplicated process for clinicians. Despite this, further clinical studies encompassing a large number of patients are necessary to determine the ability of cortical thickness to predict a physician’s subjective assessment of bone quality and fixation quality intraoperatively, the maintenance of hardware and fracture alignment on postoperative

Figure 1 Cortical thickness is measured at the illustrated levels (yellow) and is calculated as the mean of the medial and lateral cortical thicknesses (red) at these respective levels.

radiographs, and the ultimate need for reoperations related to hardware failure.

Spiral CT Spiral CT provides a practical method of assessing BMD, especially because CT scans are often used preoperatively to plan proximal humeral fracture repairs. Spiral CT has been used to determine local BMD in the spine.16,31,50 Recently, Krappinger et al24 introduced the first method of assessment of cancellous BMD of the proximal humerus using spiral CT data. The average Hounsfield unit values in standardized regions of interest of the proximal humerus were calculated; then, a linear calibration equation was

1790 Table I

S. Namdari et al. Bone mineral density prediction based on cortical thickness measurements)

Region of interest

Calculation of BMD prediction (g/cm2)

Humeral head Surgical neck Greater tuberosity Lesser tuberosity

0.10 0.14 0.09 0.11

   

mean mean mean mean

cortical cortical cortical cortical

thickness thickness thickness thickness

(mm) (mm) (mm) (mm)







Example predicted BMD if 4 mm cortical thickness 0.00 0.10 0.05 0.05

0.40 0.46 0.31 0.39

g/cm2 g/cm2 g/cm2 g/cm2

BMD, bone mineral density. ) The prediction is based on methods described by Tingart et al.61

computed to calculate from Hounsfield unit to BMD. They noted that the intraobserver and interobserver reliability was high (intraclass correlation coefficient >0.9) using this method. Krappinger et al23 followed this study with a clinical investigation that used their method of BMD assessment by CT scan and determined that patients with low local BMD are prone for fixation failure. It is unclear whether this method is easily reproducible and able to be efficiently applied by clinicians.

Augmentation of proximal humerus fractures: biomechanical and clinical data Surgical techniques for management of osteoporotic proximal humeral fractures continue to evolve because an optimal treatment strategy has yet to be discovered. Locking plates have revolutionized the management of the osteoporotic fracture but are not without complications.5,49,55 Augmentation of plate fixation with heavy, nonabsorbable sutures through the rotator cuff has become a standard addition to fixation constructs in recent years.2,46 In addition, plate designs with medial column support screws62 and polyaxial locking screws22,60 have been introduced; however, the benefits of these design changes have yet to be definitively proven. Citing complications with plate fixation, surgeons have attempted intramedullary nailing45,53 and percutaneous fixation6,33 of these injuries, with variable success. Because no true consensus exists regarding the optimal fixation strategy for these injuries, the osteoporotic proximal humeral fracture represents an unsolved problem in orthopedic care that, in our opinion, centers around poor bone quality and a corresponding inability to achieve stable fixation. Because a discussion of the different fixation methods is well beyond the scope of this review, we focus primarily on existing techniques and outcomes of allograft or autograft augmentation of proximal humerus fractures in osteoporotic patients.

Intramedullary fibular graft Intramedullary strut grafting of the proximal humerus was introduced by Walch et al61 in 1996 for nonunions of the surgical neck. In acute fracture fixation, inadequate mechanical support of the medial column has been

associated with varus collapse and complications after fixation of proximal humeral fractures. Attempts have been made to obtain adequate mechanical support by achieving an anatomic or slightly valgus-impacted stable reduction with medial cortical contact or by placing a superiorlydirected oblique locking screw in the inferomedial region of the proximal fragment (‘‘medial support screw’’), or both. Placement of an intramedullary fibular strut has been proposed as a means of creating medial cortical support in an effort to prevent varus collapse of the head. To our knowledge, 4 studies have compared the biomechnical performance of a locking plate alone and a locking plate with a fibular strut graft in a proximal humeral fracture model.3,7,35,42 Three studies3,7,35 used cadaveric specimens and 1 study42 used composite analog humeral models. All studies used a ‘‘gap model’’ (Fig. 2). In brief, an unstable proximal humeral fracture was simulated in each specimen by osteotomy using a microsagittal saw. The first osteotomy was placed in line with the anatomic neck of the humerus, and the second was placed 1 cm distal to the inferomedial aspect of the articular cartilage of the humeral head and perpendicular to the long axis of the humeral shaft. All 3 studies using the cadaveric model demonstrated superior biomechanical performance of the proximal humeral fracture models augmented with a fibula strut graft.  Bae et al3 used 14 cadavers in each group and noted that displacement was significantly less (P ¼ .031) and that all maximum failure loads (P ¼ .024) and measures of stiffness (P ¼ .035) were significantly greater in the fibular strut group than in the control group.  In a smaller study of 8 paired cadaveric limbs in each group, Chow et al7 found that no specimens in the fibular strut group demonstrated varus collapse, whereas 6 of 8 nonaugmented constructs collapsed (P < .05).  Mathison et al35 tested 6 paired cadaveric limbs in each group to determine the relative movement between the humeral head and the shaft under bending and failure loads. The fibular strut group demonstrated increased failure loads by 1.72 times (P ¼ .02), and the initial stiffness of the construct was 3.84 times greater (P ¼ .005) than the control group.35  Finally, using 10 composite analog humeri, comprising an osteoporotic-like trabecular network inside a rigid layer replicating cortical bone, Osterhoff et al42

Osteoporotic proximal humeral fractures

1791 Most recently, Nevaiser et al39 conducted a retrospective case series of 38 patients who underwent fibular strut graft augmentation by the method described by Gardner et al.14 At a mean 75 weeks of follow-up, they noted no cases of intraarticular screw penetration or cutout. The reduction was lost in 1 patient, and 1 patient was described to have partial avascular necrosis at follow-up. The mean Disabilities of the Arm, Shoulder, and Hand (DASH) score was 15 (range, 0-66.4) and the mean Constant-Murley score was 87 (range, 51-95). Further clinical study remains necessary to directly compare augmentation with fibular strut allograft and traditional locking plate techniques in like-hosts (eg, age, sex, and bone quality) with like-fractures (eg, comminution, displacement, fracture segments) to determine the true clinical benefit.

Calcium phosphate or sulfate cement

Figure 2 An example is shown of a typical ‘‘gap model’’ that is often used in biomechanical testing of proximal humeral fracture fixation.

determined fragment gap distance (intercyclic motion), fragment migration, and residual plastic deformation in samples augmented with a fibular strut graft and controls. The addition of a fibular graft to the fixation plate led to 5 times lower intercyclic motion (P < .05), 2 times lower fragment migration (P ¼ .008), and 2 times less residual plastic deformation (P ¼ .014). Despite encouraging results from these biomechanical studies, clinical investigations comparing the use of fibular strut graft augmentation with traditional locking plate techniques are lacking. Gardner et al14,15 performed 2 important clinical studies that underscored the importance of medial column support. One study found that in fractures in which no medial column support was obtained, either with anatomic reduction or with screws in the inferomedial humeral head, reduction loss and articular screw penetration occurred in 29%.15 They subsequently described their technique for intramedullary fibular strut graft augmentation to restore the medial column and presented outcomes of a small series of 7 patients.14 At a short-term follow-up of 3 to 6 months, all fractures healed without loss of reduction or fixation stability. They noted that between 3 and 4 months postoperatively, the allografts appeared to have progressive incorporation into the proximal humerus with blunting of the cortices of the fibula.

Calcium phosphate cement has been developed to enhance fixation in cancellous bone and has been used in augmentation of bone cysts, intertrochanteric hip fractures, and femoral neck fractures.11,30,36 It is injected as a paste and hardens in vivo by means of a normothermic crystallization reaction to form a carbonated apatite. The hardened calcium phosphate cement resembles the mineral phase of bone in crystallinity and chemical composition. Calcium phosphate cements can be injected or molded into small bone defects and provide structural support with good compressive strength. Kwon et al26 conducted a biomechanical evaluation of 18 paired cadaveric limbs. They used a slightly different fracture model compared with the biomechanical studies of fibular strut graft augmentation. A microsagittal saw was used to create 1 osteotomy line transecting the surgical neck and the other transecting the greater tuberosity. To simulate bone loss or comminution, the cancellous bone of the inferior third of the humeral head was manually impacted in an inferior-to-superior direction with the flat tip of a 0.25-inch rod. This left a medullary void in the inferior one-third of the humeral head. The bone fragments were then reduced anatomically and secured with 1 of 3 forms of internal fixation: a cloverleaf plate, an angled blade-plate, or Kirschner wires. Six pairs of humeri were randomly assigned to treatment with each device. One specimen in each pair was secured with internal fixation alone, whereas the other was secured with internal fixation combined with calcium phosphate cement. Supplementation with calcium phosphate cement led to significant improvements in the mechanical performance of all 3 forms of internal fixation, as demonstrated by a significant decrease in interfragmentary motion, a significant increase in torque to failure, and a significant increase in torsional stiffness. The addition of calcium phosphate cement increased the stiffness of even the most osteoporotic specimens to levels that were higher than those of the most osteodense specimens that had been treated with internal fixation alone.

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In a clinical study, Robinson and Page47 conducted a case series of 25 patients with severely impacted valgus fractures of the proximal humerus in which all were treated with open reduction with screws or buttress plate fixation and augmentation with injectable calcium phosphate (Norian, Cupertino, CA, USA) in the humeral head.47 Important to note, the surgical techniques in this study did not involve the use of locking plates but, rather, incorporated nonlocking buttress plates or cannulated screws to achieve fixation. All fractures united within the first year, all reductions were maintained, and no patient had signs of osteonecrosis of the humeral head on the latest follow-up radiographs. At 1 year, the median Constant score was 80 points and the median DASH score was 22 points. The functional results continued to be satisfactory in the 12 patients who were monitored for 2 years. To our knowledge, no biomechanical studies have evaluated calcium sulfate bone cement for augmentation of proximal humeral fractures. However, in a clinical study by Lee and Shin,28 a calcium sulfate (MIIG 115; Wright Medical Technology, Arlington, TN, USA) injection in the medial metaphyseal junction was performed in 14 patients when it was believed to be necessary to maintain the position of the reduction.28 When this group was compared with patients who were not believed to need calcium sulfate injection, the mean University of California, Los Angeles (UCLA) score of the 14 patients who received a calcium sulfate graft was 30.2 compared with 28.9 in those those who did not receive the graft (P ¼ .320). A reduction failure occurred in 1 of the 14 patients (7.1%) who received the calcium sulfate graft and in 4 of the 30 patients (13.3%) who did not receive the graft. Because augmentation was conducted in a nonrandomized fashion, it is difficult to make conclusions based on the findings of this study.

Iliac crest bone graft Ten patients with Neer type 4 impacted valgus fractures of the proximal humerus underwent biological reconstruction including open reduction, elevation of the head fragment, grafting, and suture fixation of tuberosities.1 Tricortical iliac crest autograft was used in 3 patients and lyophilized iliac allograft was used in 7. The humeral head was elevated and reduced to its anatomic position with a blunt dissector. The reduction created a cavity under the head that was supported mechanically to prevent a subsequent collapse. Radiographic and clinical results were evaluated after a mean follow-up of 38.8 months (range, 24-49 months). All fractures united within 6 to 8 weeks. The mean Constant and DASH scores were 81.5 (range, 72-90) and 23 (range, 17-38), respectively. None of the patients had signs of osteonecrosis in the humeral head. In keeping with all of the clinical studies of augmentation of proximal humeral fractures, no comparison was made with a group treated without bone grafting.

Figure 3 Postoperative radiograph shows fixation of a proximal humeral fracture using an intramedullary fibular strut graft.

Authors’ preferred approach Given the limitations of the current literature, it is impossible to provide an evidence-based algorithm for the

Osteoporotic proximal humeral fractures use of biologic augmentation in the treatment of proximal humeral fractures. However, we use the limited biomechanical and clinical data as well as our personal experience to help dictate treatment of these difficult fractures. Once the decision is made to proceed with surgical fixation with a locking plate, we assess the status of the medial cortex. If the medial cortex is intact and the combined cortical thickness on plain radiographs is >4 mm, we do not routinely use augmentation. If the medial cortex is intact and the combined cortical thickness on plane radiographs is <4 mm, we often will use an injectable calcium phosphate or crushed cancellous allograft bone chips to fill the void that often exists in the humeral head. If the medial cortex is not intact, we give strong consideration to the use of an intramedullary fibular allograft regardless of cortical thickness (Fig. 3). We do not routinely use calcium sulfate due to its more rapid resorption rate compared with calcium phosphate and do not use iliac crest autograft in cases of acute fracture fixation. Important to note, we always use suture fixation in the rotator cuff and a superiorly directed oblique locking screw in the inferomedial region of the proximal fragment (‘‘medial support screw’’) in the fixation construct. However, our guidelines for augmentation are not absolute, and we often change our clinical decision making based on multiple other factors, including fracture pattern, comminution, quality of reduction, and patient-related factors. Further biomechanical and comparative clinical studies will be necessary to create a more comprehensive, evidence-based treatment algorithm.

Conclusion The osteoporotic proximal humeral fracture represents an unsolved problem with risk of poor fixation and failure with operative treatment. The importance of the fragility fracture workup cannot be overestimated. In addition, the role of multidisciplinary osteoporosis management in the acute setting may provide benefit in fracture management and healing. Techniques for accurately determining BMD preoperatively could be beneficial in dictating the decision to treat a fracture operatively as well as the need for augmentation with bone graft. While surgical techniques continue to evolve, augmentation of these fractures with allograft, autograft, or calcium-based cements represent means to improve the biomechanical characteristics of the fixation construct and yield clinically beneficial results. Further study remains necessary to refine methods of BMD determination and to clinically compare outcomes of traditional fixation techniques with methods of augmentation.

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