The Problem

Proximal humerus fractures account for 5% of all fractures of the appendicular skeleton. Their incidence is low under the age of 40 and rises almost exponentially with age. Approximately 70-80% of proximal humerus fractures occur in females and they are the third most common osteoporotic fracture after hip and distal radius fractures. The literature suggests increasing incidence in the elderly and recent estimates suggest that the number of proximal humerus fractures may triple over the next three decades.

Overall, 75% of proximal humerus fractures are the result of low-energy domestic falls. However, when seen in the younger population, they are usually the result of high-energy trauma including car accidents, sports, gunshot wounds, and falls from heights.

The majority of these injuries are believed to occur when the shoulder sustains an impact force, leading the relatively hard bone of the glenoid to act as an anvil, fracturing the neck of the humerus. However, proximal humerus fractures also frequently occur from falls on outstretched hands. Studies have shown associations with delayed reaction times and impaired neuromuscular protective forces.

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The majority of proximal humerus fractures are treated conservatively. However, complex fractures and those with moderate to severe displacement are generally treated with surgery. Options for operative fixation are numerous, and include either open or closed reduction with fracture stabilization utilizing sutures, nails, and plates. Furthermore, the increasing use of arthroplasty for the most complex fracture patterns has made treatment decisions even more clouded. This complexity, coupled with the increasing functional expectations of an aging population, requires the surgeon to be aware of the newest techniques and trends in management.

Clinical Presentation


Proximal humerus fractures usually present acutely with pain, swelling, and deformity of the upper arm. The patient will usually report a direct force to the shoulder, a fall from standing, excessive internal or external rotation and/or axial loading. If little or no trauma is reported, tumor or infection should be considered. Upon presentation, the patient’s baseline functional status and ability to participate in rehabilitation should be determined as these may affect treatment decisions.

Physical Exam

Attention should be paid to how a patient moves and carries their shoulder. Any swelling, asymmetry, or previous scars should be noted. In severe fracture patterns and fracture-dislocations, normal shoulder contour may be lost. Open fractures are uncommon, though severely displaced fractures have been reported to cause skin breakdown and pressure necrosis. Ecchymosis is usually present and may extend from the upper medial brachium down the entire extremity. The hands should be inspected for any signs of cyanosis.


In the absence of obvious deformity, the proximal humerus should be palpated with attention paid to the acromioclavicular and sternoclavicular joints as well as the biceps tendon. Additionally, to assess for any associated injuries, the scapula, anterior glenohumeral joint, acromion, and coracoid process should be palpated for tenderness.

Range of Motion

Patients may be unable to range their shoulders secondary to pain in the acute phase of the injury. For those able to range their shoulder, movement of the fracture fragments may cause crepitus. The examiner should attempt to gently internally and externally rotate the humerus while palpating the injured shoulder. If the arm moves as a single unit, the fracture is impacted and clinically stable.


While full strength will be impaired in the setting of acute fracture, the initial clinical evaluation should include an examination of muscular strength. In particular, attention should be paid to the deltoid muscle (axillary n.), biceps muscle (musculocutaneous n.), wrist flexors (median n.), wrist extensors (radial n.) and finger abductors (ulnar n.), all of which could be affected in the setting of an associated brachial plexus injury.

Neurovascular Exam

A full upper extremity neurovascular exam should be completed on every patient. Sensation to light touch should be tested in the axillary, musculocutaneous, radial, ulnar, and median nerve distributions. Axillary nerve neuropraxia is the most common neurologic injury associated with proximal humerus fractures. Neurologic injuries are more common in those with fracture dislocations and in injury patterns where a fracture fragment is displaced medial to the coracoid process.

A vascular exam should include, at a minimum, palpation of radial and ulnar pulses and an assessment of capillary refill. If pulses are not palpable, a hand-held doppler device can be used to confirm adequate blood flow. Vascular injury, although quite rare, can occur and is difficult to detect secondary to the rich collateral circulation about the shoulder. One must have a high index of suspicion in high-energy injuries or when shaft displacement into the axilla occurs.

Associated Injuries

While most proximal humerus fractures are isolated, it is still important to assess for associated injuries. Patients reporting a high-energy mechanism need to be evaluated for spinal injuries, rib fractures, hemothoraces, and pneumothoraces. Additionally, ipsilateral fractures of the elbow, forearm, and wrist are commonly associated with proximal humerus fractures and may be masked by pain.


Patients should receive a three-view “trauma series” of the shoulder including anteroposterior (AP), lateral (“Y”), and axillary views. The AP view should be taken with the beam at a 45 degree angle from the sagittal plane, which gives the best view of the humeral head articular surface. Some patients may be unable to tolerate the axillary view due to pain. If so, a Velpeau view can be substituted by leaning the patient, who can remain in their sling, backward 45 degrees over the cassette.

If the amount of displacement cannot be determined by radiograph, or the fracture pattern is unclear, a computed tomography (CT) scan is indicated. Magnetic resonance imaging (MRI) has little utility in evaluating the acute proximal humerus fracture because CT scans provide better visualization of the fracture pattern and MRI interpretation can be distorted by altered anatomy. However, if there is persistent pain post-operatively, MRI may be useful to rule out rotator cuff pathology.

Neer Classification

It was initially recognized that the proximal humerus tends to fracture along its physeal lines of fusion. Because of this, four principle fragments (greater and lesser tuberosities, humeral head, and humeral shaft) may be produced. If any of these fragments are separated by more than 1 cm or have more than 45 degrees of angulation, they are considered displaced.

Using these definitions, Neer created a classification system that remains the most popular and clinically relevant based upon the number of parts that are fractured. While it has been criticized for lack of reproducibility and its inability to predict outcomes, it remains the most commonly used classification system. Over time, it has been modified to include additional configurations that have been found to be useful in treatment decisions or predicting outcome.

Neer Classification
  • One-part fractures

  • Two-part fractures

    Greater tuberosity

    Lesser tuberosity

    Anatomic neck

    Surgical neck

  • Three-part fractures

  • Four-part fractures

  • Fracture-dislocations

  • Articular surface fractures

Specific Fracture Types

One-Part Factures

One-part fractures are defined as fractures that are non-displaced or minimally displaced regardless of the number of fracture lines. These injuries account for approximately 50% of all proximal humerus fractures and tend to occur in younger, healthier patients.

These fractures generally have a good prognosis and most should be treated non-operatively.

Inferior subluxation (pseudosubluxation) of the humeral head can occur and is felt to be related to deltoid atony rather than ligamentous injury and will usually resolve over a few weeks. If the patient reports persistent pain and/or dysfunction, they should be evaluated for rotator cuff tear, which may have occurred with the initial fracture.

Two-Part Greater Tuberosity Fractures

Two-part fractures involving the greater tuberosity account for 10% of all proximal humerus fractures. There is generally a spectrum of severity, with isolated fractures occurring more frequently in younger patients, and fractures associated with glenohumeral dislocation occurring more in the middle-aged and elderly. It has been estimated that 10% of greater tuberosity fractures have a concomitant anatomical neck fracture, which may be missed if the AP radiograph isn’t obtained appropriately (see “Imaging” above). The most severe form of a two-part fracture, referred to as the “terrible triad” of the shoulder, occurs when a tuberosity fracture is associated with a dislocation and nerve injury.

If there is displacement greater than 10 mm (5 mm for superior displacement), these fractures should be treated operatively due to the risk of subacromial impingement, muscular weakness, and nonunion.

Two-Part Lesser Tuberosity Fractures

Two-part fractures of the lesser tuberosity are much less common than those of the greater tuberosity. Unlike other proximal humerus fractures, they are most common in middle-aged patients. Displaced lesser tuberosity fractures should be treated operatively when the fracture involves a large part of the articular surface or the fragment blocks internal rotation. These fractures are often associated with posterior shoulder dislocations.

Two-Part Surgical Neck Fractures

Two-part surgical neck fractures account for about 25% of all proximal humerus fractures. There is a low risk of osteonecrosis because the fracture mechanism generally doesn’t compromise the humeral head’s blood supply. Frequently, the humeral shaft is impacted up into the metaphysis. In these cases, the fracture is relatively stable with little risk of further displacement. If the fracture is felt to be unstable but the reduction is adequate, closed reduction followed by percutaneous screw or pin fixation may be considered.

Varus impacted fractures, however, may become more angulated with non-operative management and should be treated operatively. Completely displaced humeral heads have a higher risk of nonunion and should also undergo operative management.

Two-Part Anatomic Neck Fractures

Two-part anatomic neck fractures are extremely rare. They are hard to treat with closed reduction and have a relatively high risk of osteonecrosis. These fractures should be treated operatively unless surgery is contraindicated.

Three- and Four-Part Fractures

Multi-fragment injuries of the proximal humerus can occur in many different configurations and controversy exists regarding their management. While CT scans can help the surgeon with preoperative planning, the true extent of these injuries can only be appreciated intraoperatively.

If the humeral head is displaced, prognostic information can be derived. Valgus-impacted fractures are one of the most common multipart configurations and are associated with better prognosis, providing the humeral head isn’t overly lateralized or dislocated anteroinferiorly. In particular, valgus-impacted four-part fractures tend to have better outcomes compared to other displaced four-part fractures, an observation first made in 1991 by Jakob et al. (JBJS Br). Fractures in varus configuration, however, generally have a worse prognosis because, like two-part varus fractures, most will become progressively more angulated when treated non-operatively due to unopposed pull of the rotator cuff musculature.


Fracture-dislocations are classified as either anterior or posterior and can occur in two-, three- and four-part fractures. They are generally recognized as having relatively worse outcomes as well as a higher risk of osteonecrosis. Anterior dislocations are more common and can be divided into two types:

  • Type-I anterior dislocations: More common in young males presenting with high-energy injury mechanisms. In type-I anterior dislocations, the humeral head remains viable and capsular attachments are retained. The injury pattern is similar to that seen in patients presenting with first-time isolated anterior dislocation of the glenohumeral joint. Outcomes are generally favorable and the majority of patients should be treated with open reduction and internal fixation (ORIF).

  • Type-II anterior dislocations: More common in older females presenting with low-energy injury mechanisms. Radiographically, these injuries may be confused with valgus-impacted compression fractures. Due to the significant tearing of capsular attachments in this injury pattern, there is a higher risk of osteonecrosis. Hemiarthroplasty should be considered in older patients presenting with type-II anterior dislocations.

Treatment Decision Making

The goals of treatment are to reduce pain and restore long term function of the shoulder joint. In most injuries, both goals can be attained. In more severe proximal humerus fracture patterns, however, function may be permanently limited and the patient should be made aware of this possibility as early as possible.

The majority of proximal humerus fractures are minimally displaced and can be treated non-operatively. For displaced fractures, the treatment decision is less clear and many factors must be taken into account including fracture pattern, humeral head viability, bone quality, patient demographics, and implant limitations.

Some surgeons believe that the combined cortical thickness of the proximal humerus diaphysis can be used to assess bone quality. Using the AP radiograph, cortical thickness is first measured from both the medial and lateral cortices at the most proximal part of the proximal humerus diaphysis and again 2 cm distal to this location. The four cortex measurements are then averaged. Cortical thickness measurements <4 mm are associated with decreased bone quality.

The likelihood of humeral head ischemia is also important in determining humeral head viability, particularly when arthroplasty is being considered. Length of metaphyseal head extension (calcar) <8 mm, the loss of integrity of the medial hinge, and involvement of the anatomic neck are associated with humeral head ischemia. When combined, they have been shown to have a positive predictive value of 97% for humeral head ischemia.

Author’s General Treatment Philosophy

Because of the poor outcomes observed with non-operative management of displaced proximal humerus fractures, this author believes that, in active patients, most of these injuries should undergo operative fixation. Closed reduction and percutaneous pinning for proximal humerus fractures should be limited, since it is believed that superior reduction can be achieved with ORIF with minimal added risk.

In younger patients, restoration of function is the main goal. Because of this, anatomic reduction and stabilization with a locking plate will almost always provide for the best result. Arthroplasty should be reserved for non-salvageable fractures.

Elderly patients, however, generally have poor bone quality which makes treatment decisions more complex. Pain relief is usually the main goal of treatment. If the fracture type is felt to be stable, non-operative management with early range of motion can be considered. However, if the fracture is felt to be unstable, ORIF utilizing a locking plate represents the best option currently. Arthroplasty is offered if the fracture is non-salvageable or the humeral head is felt to be non-viable.

Non-Operative Management

The majority of proximal humerus fractures can be managed non-operatively. Absolute indications for non-operative management include minimal displacement, advanced age, medical contraindications to surgery, and dementia.

While these factors are important to consider, it is the surgeon’s perception of stability and the effect of malunion on this mobile joint that ultimately determines treatment modality. Non-operative treatment of multipart fractures and fracture-dislocations may result in significant functional impairment, stiffness, and may predispose to nonunion. Because of this, non-operative treatment of displaced or multipart fractures should only be considered in those who are contraindicated for surgery.

A sling or swathe should be used for shoulder immobilization and comfort. Hanging casts should be avoided because they may predispose to nonunion. If a patient has a stable or impacted fracture, early range of motion should be encouraged at 7 – 10 days. Pendulum exercises should be started initially followed by passive range of motion exercises. Resistance exercises can be started at 3 months. Patients should be followed with frequent radiographs to ensure reduction is maintained.

When non-operative management is pursued in those with non-displaced or minimally displaced proximal humerus fractures, patients may achieve a range of motion up to 90% of the uninjured side and the majority of patients report being satisfied with their outcome.

Operative Management

The percentage of proximal humerus fractures undergoing operative management has increased over the past decade due to an increased number of treatment options as well as improved implant technology and surgical technique. With any operative treatment, satisfactory technique, anatomic reduction, and proper patient selection are the most important factors determining success.

Closed Reduction Percutaneous Pinning

Minimally invasive treatment options, such as closed reduction and percutaneous pinning, have the major advantage of avoiding the surgical dissection required of other techniques. However, the procedure is technically challenging, particularly for more severe fracture patterns and there is a substantial complication rate reported. This technique is reserved for younger patients with better quality bone. Meticulous surgical technique is required in these cases.

Historically, this technique is thought to be most suitable for unimpacted fractures and valgus three- and four-part fractures that have significant translation of the humeral head from the shaft. It should be avoided in those with osteoporosis or a combined cortical thickness <4 mm since adequate cortical purchase is required.

First, adequate reduction should be achieved under fluoroscopy in the operating room. In addition to manipulative techniques, the use of percutaneous “joysticks” can help aid in reduction. Care should be taken to avoid injury to the axillary nerve and circumflex humeral vessels. Definitive fixation should be achieved with cannulated screws or threaded Kirschner wires.

If pins are used, sites should be identified that are sufficiently distal to ensure adequate cortical contact. The pins should be inserted in a retrograde fashion from anterolateral to posteromedial to account for the normal retroversion of the humeral head. Greater tuberosity fracture pins should be inserted superolateral to posteromedial with care taken not to advance pins past the medial cortex to avoid injuring the axillary nerve or posterior circumflex humeral vessels.

Open Reduction and Internal Fixation

Open reduction and internal fixation with plate fixation is the most commonly performed operation for the treatment of proximal humerus fractures. Advantages include the ability to achieve sufficient anatomic fracture reduction, ridged internal fixation, and the preservation of rotator cuff integrity. Disadvantages are related to the larger surgical exposure. This technique is most commonly used for salvageable two-, three-, and four-part fractures.

The approach can be performed with either a deltopectoral (DP) or extended deltoid-splitting (DS) approach. The axillary nerve should be identified and protected in the latter. The anterior portion of the deltoid insertion is usually released to expose the fracture site with the DP approach. In three- and four-part fracture dislocations, the dislocation of the head segment must be reduced prior to the fracture. Occasionally, an extended approach may be necessary in order to reduce the humeral head into the glenoid. If the fracture pattern is simple, it should be reduced and provisionally fixed with Kirschner wires. Biplanar fluoroscopy should be utilized to ensure reduction following the provisional fixation.

The decision to use a locking or non-locking pate is one that must be made on a patient-to-patient basis. Locking plates have become more popular over the past 10 years because they appear to offer a more secure fixation in osteoporotic bone. Recent reports of complications and hardware failure associated with locking plates, however, has highlighted the importance of ensuring a stable reduction and using sound surgical technique.

When the plate is placed, care should be taken to ensure it isn’t placed too proximally, which can impinge against the acromion, or too close to the biceps tendon, which may injure the anterior circumflex humeral artery.

If there is significant medial comminution, screws should be placed in the humeral head first and then the humeral shaft should be reduced to the pate in an attempt to prevent varus malalignment. Generally, four to six screws are used to reduce the humeral head and three to four screws are used distally for the humeral shaft. We believe some type of osteoconductive bone void filler should be utilized to minimize fracture settling and screw penetration.

Intramedullary Nailing

Like other minimally invasive techniques, intramedullary (IM) nailing of proximal humerus fractures has the advantage of a reduced surgical exposure. Some believe that it may also preserve periosteal blood supply. Disadvantages include the concern for rotator cuff injury at the insertion site and re-displacement of greater tuberosity fractures. It is generally used to treat simple two-part fractures. When used in complex three- and four- part fractures, a 45% reoperation has been observed.

A DS approach should be used to develop the nail entry portal. The entry point should be either through the greater tuberosity or the lateral articular surface. Minimal reaming should be necessary before placement of the rod and proximal and distal locking screws. Retrograde nailing has been reported, but there is a lack of evidence to support its routine use.

Overall, while results have been satisfactory when used in simple fractures, there is a high complication rate including malunion and hardware failure as well as rotator cuff dysfunction that frequently requires reoperation when used in more complex fracture patterns.


Arthroplasty is generally reserved for four-part fractures, three-part fractures in older adults with poor bone quality, head-splitting fractures, fracture-dislocations, and fractures involving greater than 40% of the articular surface. Delayed arthroplasty is also used to treat complications arising from fracture treatment. Hemiarthroplasty should be used over total shoulder arthroplasty unless there is degenerative joint disease affecting the glenoid.

Good outcomes are associated with anatomic healing of the tuberosities, while tuberosity nonunion or secondary displacement is associated with poor outcome. There are trauma specific implants, but they have not yet been shown to be superior. Hemiarthroplasty appears to be a good option for long term pain relief, but not for functional outcomes.

Reverse total shoulder arthroplasty (RSA) has seen increasing use in proximal humerus fractures mainly due to concerns about tuberosity healing with hemiarthroplasty. The RSA prosthesis serves to medialize the glenohumeral joint, giving the deltoid a more favorable moment arm which theoretically minimizes rotator cuff dysfunction resulting from greater tuberosity complications.

While the role of RSA in proximal humerus fractures is still being investigated, early evidence suggests it may serve a role in: (1) primary fixation when the greater tuberosity is unsalvageable and (2) for revision of failed hemiarthroplasty. Some shoulder surgeons with experience in RSA have abandoned hemiarthroplasty in favor of RSA for all proximal humerus fractures requiring arthroplasty, believing the technique offers superior results. It is likely RSA will become more common as evidence accumulates and surgeons gain experience with the technique.

The surgical approach for arthroplasty can be achieved with a DP or DS approach. Heavy, non-absorbable, braided sutures are placed through the tendon around each tuberosity. The humeral head is then excised and an implant size is chosen. Prosthetic height can be chosen based upon the location of the calcar. If fractured, the upper border of the pectoralis major insertion can be used as a guide. If not displaced, the greater tuberosity can also be used as a guide since the neck of the prostheses should lie exactly at the level of the supraspinatus insertion if the fracture is anatomically reduced. Once inserted, the prosthesis should be retroverted 20-30 degrees. Excess retroversion predisposes to secondary redisplacment of the greater tuberosity.

Overall, results for hemiarthroplasty vary. Good results are associated with younger age, hemiarthroplasty as a primary treatment (versus as a salvage), and successful tuberosity healing. Generally, most patients will have a pain-free, though weak and stiff shoulder.

Pearls and Pitfalls of Technique

Open Reduction Internal Fixation
  • A threaded pin can be used as a joystick in the posterior humeral head to aid in reduction.

  • In difficult to reduce three- and four-part fractures, sutures can be inserted into the subscapularis and supraspinatus tendons and can be used help align the fracture fragments.

  • The superior DS approach can be used for isolated greater tuberosity fractures.

Intramedullary Nailing
  • Splitting the deltoid muscle greater than 5 cm distal to the acromion risks injury to the axillary nerve.

  • The humeral canal should be reamed 1.0 to 1.5 mm larger than the nail diameter, depending on the manufacturer.

  • Retrieval of the humeral head may be aided by moving the stump of the bicipital tendon out of the surgical field.

  • A catheter can be used as a suture passer when reattaching the greater tuberosity.

Potential Complications


Can occur in up to 14% of three-part fractures and 34% of four-part fractures.


Can be caused by excessive traction, high comorbidity burden, severe displacement, poor bone quality, or infection.


Can be caused by inadequate reduction or hardware failure.

Post-traumatic Shoulder Stiffness

May be minimized with early physical therapy.


While the precise incidence is unknown, it is relatively uncommon.

Vascular Injury

Incidence of up to 6%. Injury to the axillary artery is most common.

Neural Injury

Axillary nerve injuries are relatively common. Patients with symptoms that do not improve over 2-3 months should have an electromyography (EMG) test. Brachial plexus injuries also occur in up to 6% of cases.

Chest Injury

Depending on the mechanism of injury, patients may be at risk of intrathoracic dislocation, hemothorax, or pneumothorax.

Myositis Ossificans

Uncommon. Associated with multiple attempts at closed reduction and un-reduced fracture dislocations. Also see with DS approach and delayed surgery.

Post-operative Rehabilitation

Most patients are advised to begin shoulder motion within 2 weeks post-operatively that consists of pendulum exercises and passive range of motion. Active range of motion exercises should be introduced at 6 weeks following tuberosity healing if affected. Resistive exercises can be introduced at 6-12 weeks.


Egol, KA, Kubiak, EN, Fulkerson, E, Kummer, FJ, Koval, KJ. “Biomechanics of locked plates and screws”. J Orthop Trauma. vol. 18. 2004. pp. 488-93. (Explains the biomechanics of locked plate technology and when they should be used.)

Hertel, R, Hempfing, A, Stiehler, M, Leunig, M. “Predictors of humeral head ischemia after intracapsular fracture of the proximal humerus”. J Shoulder Elbow Surg. vol. 13. 2004. pp. 427-33. (A prospective examination of 100 proximal humerus fractures. Identifies three important predictors of humeral head ischemia.)

Jo, MJ, Gardner, MJ. “Proximal humerus fractures”. Curr Rev Musculoskelet Med. vol. 5. 2012. pp. 192-8. (A recent review of proximal humerus fractures with a useful section on surgical decision making.)

Min, W, Davidovitch, RI, Tejwani, NC. “Three-and four-part proximal humerus fractures: evolution to operative care”. Bull NYU Hosp Jt Dis. vol. 70. 2012. pp. 25-34. (A helpful review of the management of multi-part proximal humerus fractures.)

Robinson, CM, Khan, LA, Akhtar, MA. “Treatment of anterior fracture-dislocations of the proximal humerus by open reduction and internal fixation”. J Bone Joint Surg Br. vol. 88. 2006. pp. 502-8. (Describes the different types and best treatment options for anterior fracture-dislocations.)

Rockwood, CA, Wilkins, KE, Beaty, JH. “Rockwood and Green’s Fractures in Adults”. 1996. (An authoritative guide to the workup and management of proximal humerus fractures. However, it is lacking newer evidence and techniques.)

Rothberg, D, Higgins, T. “Fractures of the proximal humerus”. Orthop Clin North Am. vol. 44. 2013. pp. 9-19. (Another helpful review of proximal humerus fracture workup and management.)

Roux, A, Decroocq, L, El batti, S. “Epidemiology of proximal humerus fractures managed in a trauma center”. Orthop Traumatol Surg Res. vol. 98. 2012. pp. 715-9. (A review of the epidemiology of both operative and non-operative proximal humerus fractures.)

Schmidt, A. “Orthopaedic Knowledge Update, Trauma 4”. American Academy of Orthopaedic Surgeons. 2010.

Solberg, BD, Moon, CN, Franco, DP, Paiement, GD. “Surgical treatment of three and four-part proximal humeral fractures”. J Bone Joint Surg Am. vol. 91. 2009. pp. 1689-97. (Another recent review of the management of multi-part proximal humerus fractures.)


Proximal humerus fractures are relatively common injuries to the shoulder, particularly in elderly females, that can lead to significant morbidity. Most minimally displaced proximal humerus fractures can be treated non-operatively; however, controversy surrounds the optimal management of displaced fractures. Open reduction and internal fixation with a locking plate is used for the majority of displaced fractures, but IM nailing, hemiarthroplasty and reverse total shoulder arthroplasty may be used in certain situations. Though the incidence of proximal humerus fractures may as much as triple over the next decade, long-term evidence to guide treatment decisions is lacking. Current management trends will undoubtedly change as implants improve and surgeons gain experience with new techniques.