Scaphoid - All about fractures of the keystone of the wrist

Percutaneous Fixation of Scaphoid Fractures
Andrew P. Gutow, M.D.
Department of Orthopedic Surgery
Palo Alto Medical Foundation
Palo Alto, California

ABSTRACT

Recent advances in techniques and implants have led to renewed interest in percutaneous screw fixation of acute scaphoid fractures. The closed cast treatment of acute scaphoid fractures generally has good outcome with bony union resulting; however, it can result in nonunion, malunion, cast induced stiffness, and lost time from employment and avocations. Acute percutaneous fixation of scaphoid fractures has been proposed as a means to avoid some of the complications of closed cast treatment. Series of acute percutaneous treatment of both non-displaced and displaced scaphoid fractures have recently been reported with close to 100% union rate with minimal complications. Techniques have been described for fixation of scaphoid fractures with headless compression screws via both volar and dorsal starting points with reduction and alignment assessed using fluoroscopy or arthroscopy. Appropriately performed acute percutaneous internal fixation is now a treatment option for a selected group of patients with acute scaphoid fractures.


HISTORY

The ideal management of scaphoid fractures has not yet been determined. The basic issues which still confound us today of diagnosis as well as complications and limitations of treatment were noted a century ago by MacLennan. Writing in 1911 he noted a “[f]racture of the scaphoid is hitherto been regarded as a rare accident, but it is, on the contrary, comparatively common. It is, however, often undetected, and a diagnosis of sprained wrist is accepted as explaining the symptoms.” Touching on our current concerns regarding internal fixation, he further wrote that “the wiring of fragments is seldom practicable; it takes time and really causes considerable interference with the surrounding structures.” (MacLennan 1911)



Fig 1

from: Streli R: Percutaneous screwing of the navicular bone of the hand with a compression drill screw (a new method). (Authors translations). Zentralbl Chir 1970 Sep 5;95(36):1060-78
Example of percutaneous (minimal incision) volar fixation by Streli with cannulated headed screw. The problem of scaphoid fracture today are the same as a century ago: that without adequate treatment there is a risk of non union and its sequalae, but with treatment there are complications of immobilization and of internal fixation. Moreover, these fractures occur in a young working population so the morbidity of the treatment itself in terms of time off work and activities is significant. Epidemiologic studies show scaphoid fracture occur at an average age of 25 year, with 82 percent of the fractures in males, with an incidence of 23-43 per 100,000 people per year (Hove 1999,Larsen 1992, van der Molen 1999). These patients prefer not to spend prolonged periods of time in a cast with the added risk of needing surgery at the end of the cast treatment.

Various surgeons have wrestled with these opposing issues throughout the 20th century and the beginning of the 21st century. Unrecognized and under treated scaphoid fractures are prone to non union which can range from 5-30% with closed cast treatment. Even fractures treated to successful union with a cast can result in radiographic arthritis or subjective wrist pain due to malunion (Amadio 1989. Jiranek 1992, Duppe 1994, Fernandez 1998, Lynch 1997 Saeden 2001)

In the 21st century, with the recent advances in the techniques of percutaneous internal fixation of scaphoid fractures, the question for patients and clinicians is for what patients does the risk benefit analysis of acute percutaneous internal fixation, make acute fixation a better choice than closed cast treatment

PERCUTANEOUS FIXATION

Percutaneous fixation of scaphoids with cannulated screws followed soon after initial reports of open reduction and internal fixation of scaphoids with solid screws (MacLaughlin 1954, Streli 1970). The first described percutaneous fixation of scaphoids was performed in Germany by Streli starting in 1962 using a cannulated but headed screw (Streli 1970) (Fig. 1)

A large series of over 200 cases using this same technique was subsequently reported by Wozasek in 1991 with an 89% union rate for acute fractures (Wozasek 1991). The 11 % non union rate may have been due to the limitations of the radiographic imaging available and the limits on ideal placement and compression with the solid headed lag screw utilized.

The advent of the headless compressions screw as developed by Timothy Herbert and then the modification of this to a headless cannulated screw by Terry Whipple, Randy Huebner and others, combined with better fluoroscopic imaging to allow for improved positioning of screws in scaphoids and compression of the scaphoid. (Inoue 1997, Whipple 1995, Haddad 1998, Slade 2001). With the use of a headless compression screw, Streli’s technique could be altered to include insertion through an articular surface. Streli performed his insertion with traction assistance with the thumb hung from a finger trap to place it in the field of the imaging device. Whipple pioneered the idea of using arthroscopy to assist in reduction (Whipple 1995), and developed a cannulated headless screw to allow for percutaneous insertion. Streli’s technique of traction assisted volar fixation was modified by Goddard (Haddad 1998), with the use of a headless cannulated screw which allowed insertion throught the scaphoid trapezoid joint if needed. Others used this same volar approach without traction with the wrist extended on an arm board ( Ledoux 1995, Inoue 1997, Bond 2001). Using a headless cannulated screw, Slade pioneered dorsal percutaneous fixation using the concept of the ring sign of the flexed scaphoid to guide in wire placement and to assist in central placement of the screw (Slade 2001). (Figure 2)

The overall results of recent series of percutaneous fixation of scaphoid fractures has been a 100% union rate for surgically fixed fractures from both the volar and dorsal approach (Table 1). Prospective randomized studies comparing acute fixation to closed cast treatment





Fig 2 (Courtesy A. Gutow)
Stable minimally displaced scaphoid waist fractrure treated with dorsal percutaneous fixation via minimal incision with healing at 8 weeks.
for stable fracture has shown the surgically fixed fractures to have faster rate of healing and earlier return to work (Table 2). (Bond 2001, Adolfsson 2001).

CLASSIFICATION and STABILITY

A classification system which separates stable from unstable and aligned from malaligned fractures can help one choose the best treatment. The location and orientation of the fracture as described in the Russe system is important to treatment (Fig. 3a) (Russe 1960). However, the key issues to choice of treatment are stability, displacement and alignment which are better delineated both by Herbert’s and Cooney’s systems (Herbert 1984, Cooney 1980, Cooney 2003) . Herbert’s classification focused on the issue of stability with his acute stable fractures (Type A) and his acute unstable fractures (Type B) (Fig. 3b).
Table 1 Outcome of Series of Percutaneous Fixation of Scaphoid Fractures

Authors Approach Implant Union Rate

Streli Volar Minimal Access Headed Cannulated Screw 70% (7/10)
1970 Traction Assisted 6 Delayed Unions
4 Pseudoarthrosis

Wozasek Volar Minimal Access Headed Cannulated Screw 89%
1991 Traction Assisted 146 Acute
81.8%
33 Delayed and Non Unions

Ledoux Volar Minimal Access Headless Solid Variable Pitch 100%
1995 (Herbert Screw) 19 Acute
4 Non Unions

Inoue Volar Minimal Access Headless Solid Variable Pitch 100%
1997 (Herbert Screw) 40 Acute

Haddad Volar Percutaneous Headless Cannulated Variable Pitch 100%
1998 Traction Assisted (Acutrak) 15 Acute

Schadel-Hopfner Volar Percutaneous Headless Cannulated Variable Pitch 100%
2000 Arthroscopic Assisted (Herbert Whipple) 22 Acute

Yip Volar Minimal Access Headed Cannulated Screw 100%
2002 3.5 mm Cannulated 46 Acute

Slade Dorsal Percutaneous Headless Cannulated Variable Pitch 100%
2002 Arthroscopic Assisted (Acutrak) 18Acute
9 Delayed

Slade Dorsal Percutaneous Headless Cannulated Variable Pitch 100%
2003 Arthroscopic Assisted (Acutrak) 15 Non unions

Table 2 Outcome of Prospective Randomized Series of Treatment of Acute Scaphoid Fractures

Authors Approach/ Implant Union Rate
Fracture Type for Surgically
Treated

Bond Volar Percutaneous Headless Cannulated Variable Pitch 100%
2001 Stable Non displaced (Acutrak) 11 Acute

Adolfsson Volar Percutaneous Headless Cannulated Variable Pitch 100%
2001 Stable Non displaced (Acutrak) 25 Acute

Herbert’s Classification


Fig. 3b
The exact amount of displacement or loss of alignment which connotes instability has not been shown; however, the criterion detailed in Cooney’s system seem best supported by clinical series which show higher rates of non union with cast treatment of the unstable fractures (Fig 3c). Cooney defines instability for scaphoid waist fracture as a step off (1mm or greater), significant comminution, or angulation as evidenced by internal scaphoid mal-alignment or carpal mal-alignment (Cooney, 1980, Weber 1980). Proximal pole scaphoid fractures are also included in the unstable group by Cooney, which classification is supported by the up to 30% non union rate for proximal pole fractures treated in a closed manner (Slade 2002).
Cooney’s Classification

Acute Stable
Displacement less than 1mm
Normal Intercarpal alignment
Distal Pole Fractures

Acute Unstable

Displacement greater than 1mm
Lateral Intrascaohoid angle > 35 degrees
Bone loss or comminution
Perilunate fracture
DISI alignment

Proximal Pole fractures

Fig. 3c

Russe’s Classification

Horizontal Oblique Transverse Vertical Oblique

Fig. 3a

Herbert’s Classification

Type A ‘Stable’ Acute Fractures
A1 Tubercle fractures
A2: Incomplete waist crack fractures

Type B ‘Unstable’ Acute Fractures
B1 Distal third oblique fracture
B2 Complete Displaced or Mobile Waist
B3 Proximal Pole fracture
B4 Trans Scaphoid Carpal Fxt / Dislocation
B5 Comminuted

Type C Delayed Union

Type D Established Non Union
D1 Fibrous Non Union (stable)
D2 Displaced Non Union (unstable)

Fig. 3b

For unstable fractures and for the mal aligned fractures both reduction and internal fixation are needed to prevent both non union and mal union, so in these cases it is a less difficult decision of


percutaneous versus open fixation. It is the stable fractures for the choice of percutaneous fixation versus cast therapy is more difficult, because adequate cast immobilization, generally results in successful union over 95% of the time .


DIAGNOSIS

From: Wheeler, 1998
Fig. 5
Effect of Screw Size and Type on Compression and Pullout strength for commonly used screwsMost fractures can be diagnosed by the history of injury, the presence of pain with palpation over the scaphoid and with plane radiographs. The standard views of the wrist as well as the posterior anterior scaphoid view with the wrist in ulnar deviation and 45 degrees of extension can be augmented by more scaphoid specific view of Ziter (Figure 4 ) (Ziter 1973). However a computed tomography (CT scan) will often show greater displacement than is appreciated on plane radiograpohs and can help assess for the exact amount of step and in checking for loss of intra scaphoid and intra carpal alignment. MRI is helpful to diagnoses occult acute fractures and in assessing for osteonecrosis of non unions. However, acute fractures requiring MRI for diagnosis are inherently so stable that if adequate immobilization is maintained they should all heal with 6-8 weeks of simple short arm casting, several weeks of which may have elapsed prior to diagnosis.



IMPLANT TYPES

In choosing an implant for fixation of scaphoid fractures one has to balance the benefits of rigidity and compression which are increased by implant diameter and changes in implant thread design, against the difficulties of placing a larger implant and the damage to surrounding structure inherent in placing a large implant. The treatment of non unions with wires combined with casting show that wires alone can provide adequate rigidity to allow for scaphoid healing if supplemental immobilization is used (Stark 1988); however, early mobilization requires rigid screw fixation.
Authors are divided on the need for supplemental immobilization following internal screw fixation. Some authors feel that supplemental casting is needed after internal fixation (Cooney 2003), while others favor rapid conversion of an operative splint to a removable splint to allow early mobilization and controlled loading (Slade 2002).
A variety of compression screws are available with the salient differences being headed versus headless design, cannulated versus solid, fully versus partially threaded, screw diameter and the method of applying compression (Fig. 5).


Fig. 4
From: Ziter FM Jr A modified view of the carpal navicular. Radiology. 1973 Sep;108(3):706-7.

Technique of Ziter for elongated Scaphoid view
For percutaneous or minimal incision fixation a cannulated screw is preferred because modern cannulated screws provide adequate rigidity for fixation of scaphoids with the advantage of better control over placement which a guide wire allows. Current technology has made headless screws the preferred implant for percutaneous fixation, as the headless design allows for the screw to be buried fully in the bone allowing implantation through a joint (either the radio carpal joint proximally or the scaphoid trapezial joint distally) and obviating such problems as erosion of the head of the screw into the surrounding bone (as seen with distally placed screw heads eroding into the trapezium) (Yip 2002).

Partially threaded screws such as the Herbert Whipple screw have a theoretical advantage over fully threaded screws such as the Acutrak screw due to the avoidance of screw threads crossing the fracture site. However, a comparison of compression generating showed the fully threaded screws have generate greater compression and resist pull out more than partially threaded screws. This is probably due to the greater bone surface contact area achieved with full threads (Wheeler 1998). Studies by Toby and others have shown that rigidity and resistance to failure due to cyclic loading is proportional to the radius to the fourth power (r^4) of the screw with larger diameter implants having the greatest resistance to failure (Toby 1997), thus arguing for the use of the largest screw which can be fit inside the bone, However, some surgeons have expressed concerns regarding the size of the hole which a larger size screw might make in the radial carpal articulation if inserted from proximally (Figure 6). To date this concern regarding possible radio carpal arthrosis has not been seen to be an issue in clinical series. Variable pitch cannulated screw designs such as the Herbert or Acutrak provide compression via a fixed variable pitch. Newer designs such as the TwinFix cannulated (Figure 7) screw allow for the surgeon to select the


Fig 6 Courtesy of A. Gutow
Clinical View of Large Diameter Screw shows size of trailing end of standard (large) acutrak screw in proximal pole of scaphoid

Fig 7 Courtesy Stryker Liebenger

Twinfix screw with independently rotating proximal and distal threads
amount of compression applied via independent rotation of the proximal and distal threads. This greater control of the amount of compression applied may have benefit in the treatment of non unions and severely comminuted fractures as the surgeon can prevent over shortening of the bone by exactly controlling how much the fracture site is compressed. Such fine control of the amount of compression may not make a difference in the fixation of more stable acute fractures.

SCREW POSITION

The position of the implant in the scaphoid is very important to the success of internal fixation, with position more important in less stable fractures and less important in more stable fractures (Figure 8). For waist fractures, clinical studies have shown a higher union rate and cadaver studies greater resistance to failure under bending loads for screws placed in the central third of both the
Fig 8

Placement of the screw in the central third of both poles of the scaphoid provides for the most screw threads in each fragment and improves the chances for and rapidity of healing,.

proximal and distal poles (Trumble 2000, McCallaster 2003). The greater strength of central position may be more a function of the fact that a centrally place screw has more threads across the fracture site in both poles than a function of the cancellous bone quality in the center of the scaphoid which may be less strong than the peripheral cortex. Biomechanical testing of proximal pole fractures has shown that fixation from proximal to distal provides greater resistance to bending failure probably because of the ability to engage more of the small proximal piece when fixing from proximally (Slade 2000). Surgeons have shown slightly greater ease in placement of screws centrally from the dorsal approach than from the volar side, but the clinical significance of this is not clear for waist fractures (Gutow 2003, Chan 2004).

ANATOMY

Percutaneous fixation requires knowledge of bone anatomy as well as of the surrounding tendons, nerves and vessels. Clinical series and cadaver dissections have shown both dorsal and volar percutaneous approaches to be safe if attention to technique is maintained ( Kamineni 1999). (Figure 9). With either approach, incision of the skin, followed by spreading down to bone



Fig 9

Volar dissection showing entry point through proximal aspect of thenar muscles.

Dorsal dissection showing starting point through distal aspect of extensor retinaculum between 2nd and 4th compartments.
volarly or the capsule dorsally prior to drilling will prevent injury to crossing structures. Volarly a small terminal branch of the radial nerve can be at risk. The starting point at the scaphoid trapezial joint through the proximal thenar muscles is safely distant from the median nerve motor branch and radial artery. Dorsally the starting point is just proximal to the standard 3-4 radio carpal arthroscopy portal. To avoid tendon injury spreading down to the joint is needed, and opening of a few millimeters of the distal extensor retinaculum may also be needed.

TECHNIQUES (Fig. 10)

Streli first treated scaphoid delayed unions and pseudoarthrosis with a volar percutaneous approach beginning in 1962. He suspended the hand by the thumb so as to allow radiographic imaging and obtained orthogonal views by pronating and supinating the forearm. A small incision was made over the distal pole of the scaphoid, a 1 mm guide wire was placed and then he overdrilled and placed a headed partially threaded cannulated compression screw. In this series of 10 cases, there was healing reported in 5 of 6 cases of delayed unions and 2 of 4 cases of established pseudoarthrosis,. Wozasek modified Streli’s technique to include percutaneous bone

Dorsal Wrist Flexed on Arm board


Courtesy A Gutow
Fig 10d

Technique of Slade Modified by Gutow and McGillivary

Various Percutaneous Approaches

Volar Traction Assisted

Courtesy N Goddard
Fig 10a

Technique of Streli modified by Goddard


Volar Extended Wrist

from Bond, Shin et al 2001
Fig 10b

Technique of Inoue modified by Bond and Shin






Dorsal

Dorsal Arthroscopic Assisted




Courtesy J Slade
Fig 10c
Dorsal Technique of Sladegrafting of established non unions, but did not begin this grafting until part through his published series (Wozasek 1991). He described using a headed screw with a washer with a 4.8 mm diameter thread and a 2.9mm core diameter. In 280 cases spanning a 15 period from 1969 through 1984, there was an 89% healing rate for acute fractures, a 81.8% rate for delayed unions and a 42.8% healing for cases of sclerotic nonunion.
The use of a headless variable pitch screw for minimal incision or percutaneous fixation was first reported by Ledoux in 1995 and Inoue in 1997, both using the solid Herbert screw (Ledoux 1995, Inoue 1997). Both authors achieved 100% union in a total of 63 cases approached via a small volar incision. Inoue positioned the wrist in extension over towels and made an 1 cm incision over the volar scaphoid and opened to the scaphoid-trapezial joint. A 1.2 mm guide wire was used to find the correct screw path and determine screw length. This was then removed and drilling was performed down the same path with the free hand insertion of the Herbert screw down the drill path.
Fig. 11

Removable splint placed following percutaneous fixation, worn until union occurs, but removed for daily range of motion exercises.


Fig 12

In cases with comminution or questions regarding healing a CT scan be helpful to decide when at allow unprotected activity. CT scan shows healing of dorsal cortex prior to volar cortex following pecutaneous fixation of comminuted scaphoid fracture.Whipple developed a cannulated version of the headless variable pitch Herbert screw to allow for more accurate percutaneous screw placement and arthroscopic assisted reduction (Whipple 1995). The use a headless cannulated screw with placement of a percutaneous guide wire from the volar approach was popularized by several authors during the late 1990s and early 21st century. Goddard reported a modification of Streli’s traction assisted volar approach and minimized the incision with use of a large 12 gauge needle to open up the scaphoid-trapezial joint and aid in the placement of the guide wire. Goddard also reported that the application of traction to acute fractures can help realign displacement. Most other authors used a modification of Ledoux’s and Inooue’s method with the wrist extended on towels, with the imaging device above and below the armboard.
Slade adopted Whipple’s technique of arthroscopic assistance to a dorsal percutaneous approach believing that the central axis of the scaphoid was better found via a dorsal starting point, especially for proximal pole fractures (Slade 2002). Using both fluoroscopic and arthroscopic control Slade also has shown how to perform reduction of displace fractures with percutaneous wires (Slade 2002). This technique of dorsal access for fixation has also been modified to a minimal access (.75 cm incision) method which allows for easier placement of the guide wire in the starting point in the proximal pole (Gutow 2003).
All author have reported good success in achieving union and with rapid return of wrist function with both volar and dorsal techniques as long as attention is paid to avoid complications.

Most surgeons performing percutaneous fixation of acute fractures recommend a program of rapid mobilization for acute fractures, with
application of a volar forearm splint or thumb spica at the time of surgery and then use of a
removable thumb spica splint until union is proven (Fig. 11). CT scan can be helpful in
determining when union has occurred, especially in cases with comminution (Fig. 12)





COMPLICATIONS OF PERCUTANEOUS FIXATION

Complications can of percutaneous fixation can be divided into injuries to the surrounding structures and incorrect placement of fixation. Damage to surrounding structures can be
avoided by careful spreading down to the tubercle when approaching volarly and spreading down to the capsule dorsally. Placement of fixation must be down the central axis for best strength and to avoid penetration into the scaphoid capitate joint, so double checking of the guide wire position in multiple views is required. The screw length should be 4 mm less than the measured length of the scaphoid to allow for complete implantation of the screw in the bone. Too long a screw can also lead to distraction of the fracture by the tip of the screw pushing against the far cortex as the attempts are made to bury the trailing edge of the screw in the bone. Displacement of fractures during screw implantation can be prevented by the placement of a second anti rotation wire prior to drilling and screw placement.

SUMMARY
Percutaneous fixation of scaphoid fractures can be an effective method of assuring aligned union of scaphoid fractures and allowing patients more rapid return to work and avocation than closed cast treatment or open internal fixation. For stable fractures., the major advantage of acute percutaneous fixationis more rapid return to activities, while for unstable fractures, percutaneous fixation can allow for a higher union rate as well as faster rehabilitation.
The choice of a volar or dorsal approach is still a matter of surgeon preference except in the cases of proximal pole fractures which should be approached dorsally. The dorsal approach violates the radio carpal joint while the volar approach is via the scaphoid trapezial joint, but no clinical effects have been shown from either approach.



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