The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 89, Issue 1

Scientific Articles | January 01, 2007

Safe Zone for the Placement of Medial Malleolar Screws

John E. Femino, MD¹; Brian F. Gruber, MD²; Madhav A. Karunakar, MD²

¹ Department of Orthopaedic Surgery, University of Iowa, 200 Hawkins Drive, 01016 JPP, Iowa City, IA 52242-1088
² Department of Orthopaedic Surgery, University of Michigan, 1500 East Medical Center Drive, Taubman Center 2914, Ann Arbor, MI 48109-0328. E-mail address for M.A. Karunakar: mkarun@umich.edu

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Disclosure: The authors did not receive grants or outside funding in support of their research for or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

Investigation performed at the Department of Orthopaedic Surgery, University of Michigan, Ann Arbor, Michigan

The Journal of Bone and Joint Surgery, Incorporated

J Bone Joint Surg Am, 2007 Jan 01;89(1):133-138. doi: 10.2106/JBJS.F.00689

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Abstract

Background: Hardware placement for fracture fixation can put soft-tissue structures at risk for injury or abutment. The prominence of the hardware is a frequent cause of pain after the fixation of ankle fractures. This study was designed to assess the risk of injury or abutment of the posterior tibial tendon with the placement of medial malleolar screws.

Methods: Ten unmatched cadaveric limbs that had been disarticulated at the knee were used, and the medial malleolus was exposed by dissection of the skin. With use of fluoroscopy and direct visualization of the deep fascia, three Kirschner wires were placed through the tip of the medial malleolus and directed parallel to the medial articular surface. The first wire was placed in the center of the anterior colliculus. Two additional wires were placed parallel and posterior to the initial wire at 5-mm intervals. The wires were overdrilled, and 4.0-mm screws were inserted over the Kirschner wires. The specimens were dissected to inspect for trauma and the proximity of the screws to the posterior tibial tendon. The medial malleolus was divided into three zones on the basis of anatomic landmarks. Zone 1 is the anterior colliculus; Zone 2, the intercollicular groove; and Zone 3, the posterior colliculus.

Results: Screws placed in Zone 1 (the anterior colliculus) did not contact the posterior tibial tendon in any specimens. Screws placed in Zone 2 (the intercollicular groove) were, on the average, 2 mm from the posterior tibial tendon. Screws placed in Zone 3 (the posterior colliculus) resulted in tendon abutment in all ten specimens and in tendon injury in five of the ten specimens.

Conclusions: Screws inserted posterior to the anterior colliculus place the posterior tibial tendon at significant risk for injury or abutment.

Clinical Relevance: On the basis of these results, we recommend direct visualization of the posterior tibial tendon prior to the placement of screws in the medial malleolus when they are inserted posterior to the anterior colliculus.

Figures in this Article

Ankle fractures are among the most common operatively treated skeletal injuries¹. Open reduction and internal fixation is generally recommended for unstable bimalleolar and trimalleolar fractures^1-4. Substantially displaced, isolated medial malleolar fractures with joint incongruence are less common, but they may also be treated surgically. The most common fracture pattern treated surgically involves a supracollicular medial malleolar fracture that begins at the shoulder of the medial tibial plafond and extends obliquely upward to the medial cortex⁵. Various techniques have been described for operative stabilization of the medial malleolus, including two 4.0-mm partially threaded lag screws, tension-band wiring, and bioabsorbable implants^6-12. The most common medial malleolar fixation technique is with 4.0-mm partially threaded, cancellous lag screws placed perpendicular to the fracture line, starting at the most inferior portion of the medial malleolus^6,9,10.

Outcomes after operative stabilization of ankle fractures are overall considered to be good. However, ankle pain after operative stabilization may be one reason for patient dissatisfaction^1-4. Soft-tissue irritation secondary to prominent hardware can be one source of ankle pain, perhaps necessitating hardware removal^13,14. Hardware-related pain can be due to multiple factors including subcutaneous positioning, impingement of bone, or irritation of deeper soft-tissue structures. The posterior tibial tendon is intimately apposed to the medial malleolus, passing directly posterior and inferior to it (Fig. 1), and it is therefore a structure likely to be affected by the placement of medial malleolar hardware. We present an anatomic cadaver study, which defines a "safe zone" for hardware placement, and suggest a technique for the placement of medial malleolar screws that avoids damage to or irritation of the posterior tibial tendon.

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Fig. 1: An undissected specimen of the medial aspect of the ankle with the fascia intact. The posterior tibial tendon (a) is intimately held against the posterior and inferior surfaces of the medial malleolus (b).

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Fig. 2: Specimen with the flexor retinaculum, superficial deltoid, and deep deltoid ligaments removed. The posterior colliculus (a) acts as a pulley for the posterior tibial tendon (b).

The regional anatomy of the medial malleolus and posterior tibial tendon, that is, the ligaments and osseous structures that compose the medial side of the ankle, has been described by several authors^15-18 and comprehensively by Sarrafian¹⁹. The osseous landmarks are the anterior colliculus, posterior colliculus, intercollicular groove, posterior tibial groove, and the medial articular facet.

The anterior colliculus is narrower and extends more distally than the posterior colliculus. It is the site of attachment for the tibionavicular, tibiocalcaneal, and superficial tibiotalar ligaments. These three ligaments are contiguous and compose the superficial deltoid ligament. The deep deltoid ligament most commonly comprises the deep anterior talotibial ligament and the deep posterior talotibial ligament. The deep anterior talotibial ligament originates from the intercollicular groove and anterior colliculus and is contiguous with the deep posterior talotibial ligament. The deep posterior talotibial ligament originates primarily from the intercollicular groove and the posterior colliculus. The posterior tibial muscle originates from the deep posterior compartment of the leg, taking origin from the distal third of the tibia and the interosseous membrane. The posterior tibial tendon has insertions on the midfoot and forefoot with the primary insertion on the medial aspect of the tarsal navicular. As the posterior tibial tendon courses behind the medial malleolus, it lies directly against the posterior tibial groove (Fig. 2) and courses beneath the posterior colliculus and medial to the deep deltoid ligament. The surface of the posterior tibial groove and the inferior aspect of the posterior colliculus serve as a pulley for the posterior tibial tendon and have a smooth fibrocartilage surface for the tendon to glide over (Fig. 3). The flexor retinaculum retains the tendon in this location as it blends with the posterior tibial tendon sheath and the superficial deltoid ligament. The action of the posterior tibial tendon is crucial to normal hindfoot function as it is the sole inverter of the foot while in foot-flat position.

Materials and Methods

Materials and Methods | Results | Discussion | References

Ten atraumatic, unmatched fresh-frozen cadaveric ankles were used. The specimens consisted of limbs, which had been disarticulated at the knee, from six male and four female donors with an average age of fifty-five years (range, thirty-nine to eighty-seven years). There were five right and five left limbs. The following assumptions were made to standardize our technique: (1) the center of the anterior colliculus represents the ideal starting point for the first screw since it is farthest (most distal) from the fracture line and possesses a hard cortical surface that would support a compression screw, (2) screws should be placed perpendicular to the medial malleolar fracture to optimize the effect of compression, (3) an oblique supracollicular fracture represents the most common fracture pattern treated with two cancellous screws, and (4) a triple guide (Zimmer, Warsaw, Indiana) represents a commonly used clinical aid for obtaining parallel screws at the closest reasonable spacing (5 mm), allowing for a bone bridge of approximately 1 mm between screws.

A 10-cm longitudinal incision was centered over the medial malleolus. Skin flaps were mobilized, and the deep fascia was exposed. Care was taken not to disrupt the flexor retinaculum over the posterior tibial tendon. With use of fluoroscopic guidance to visualize the contours of the medial malleolus, with the foot in neutral position, a 1.6-mm Kirschner wire (Zimmer) was placed with use of a triple guide through the superficial deltoid ligament into the center of the anterior colliculus. The lateral view was used to ensure that the Kirschner wire was placed through the center of the anterior colliculus and nearly parallel to the anterior tibial cortex. Anteroposterior and mortise radiographic images were made to confirm that the Kirschner wire was placed in the center of the malleolus and parallel to the medial articular facet. Two additional Kirschner wires were placed posterior and parallel to the initial wire at 5-mm intervals, as determined by the triple guide (Fig. 4). The Kirschner wires were then overdrilled, and three 4.0-mm partially threaded screws were placed and fully seated against the cortical bone.

The screws were then exposed by dissecting the superficial and deep deltoid ligaments. The posterior tibial tendon was evaluated for evidence of surgical trauma and screw abutment. Tendon damage was defined as abrasion, laceration, or direct penetration of the posterior tibial tendon. Measurements were made with electronic calipers (Medtronic Sofamor Danek, Memphis, Tennessee) to quantitate the proximity of the posterior tibial tendon to the two most posterior screws. The distance from the anterior colliculus to the intercollicular groove was measured for each specimen. The medial malleolus was divided into three zones on the basis of anatomic landmarks. Zone 1 includes the anterior colliculus; Zone 2, the apical portion of the intercollicular groove; and Zone 3, the posterior colliculus (Fig. 5). The number of injuries to the posterior tibial tendon and the contact of the hardware with the tendon were recorded. A chi-square analysis was performed, and a p value of <0.05 was considered significant.

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Fig. 3: The fibrocartilage gliding surface of the posterior tibial groove and posterior colliculus is noted between the black lines. The posterior tibial tendon (a) is retracted posteriorly.

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Figs. 4-A and 4-B: Anteroposterior radiograph of the ankle with the three Kirschner wires placed at the most inferior tip of the medial malleolus and nearly parallel to the medial articular facet. Lateral radiograph of the ankle with the Kirschner wires in place. The most anterior Kirschner wire is in the center of the anterior colliculus. The middle Kirschner wire is in the intercollicular groove and the most posterior Kirschner wire is in the posterior colliculus.

Results

Materials and Methods | Results | Discussion | References

The anterior screw was not in contact with the posterior tibial tendon in any specimens, and its placement was not associated with tendon damage in any specimens. The middle screw was an average of 2 mm (range, 0 to 4 mm) from the posterior tibial tendon and was found to be in direct contact with the posterior tibial tendon in four of the ten specimens. The distance from the anterior aspect of the anterior colliculus to the center of the intercollicular groove was an average of 12 mm (range, 11 to 15 mm). This meant that, in smaller specimens, the middle screw was placed in the posterior aspect of the intercollicular groove as determined by our choice of the center of the anterior colliculus as the ideal starting point and by the 5-mm spacing dictated by the triple guide. The most posterior screw was found to be in contact with the posterior tibial tendon in all ten specimens (Fig. 6). Posterior tibial tendon damage from hardware placement in this location was identified in five of the ten specimens. Zone 3 had significantly higher rates of injury and contact compared with Zones 1 and 2 (p < 0.001 for both).

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Fig. 5: A diagram of the lateral aspect of the ankle showing the three zones of the medial malleolus. The so-called safe zone, Zone 1, is clearly defined within the anterior colliculus.

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Fig. 6: A study specimen after the medial malleolar screws had been placed and the superficial and deep deltoid ligaments had been removed. The most posterior screw (hemostat), in the posterior colliculus, is found to abut the posterior tibial tendon.

Discussion

Materials and Methods | Results | Discussion | References

The operative fixation of a supracollicular medial malleolar avulsion with either a partially threaded cancellous screw and Kirschner wire or two partially threaded cancellous screws is a widely accepted clinical practice. Descriptions of the operative technique for the placement of hardware into medial malleolar fractures have not, to our knowledge, included the specific recommendations to avoid potential risk to the posterior tibial tendon as it courses directly posterior and inferior to the medial malleolus.

Posterior tibial tendon problems after ankle trauma have been described. Holmes and Mann suggested that previous trauma to the ankle may be an etiologic factor in the development of posterior tibial tendon insufficiency, leading to an acquired flat foot²⁰. Damage to the posterior tibial tendon has also been reported to occur at the time of the initial trauma²¹. In addition, operative fixation can place the posterior tibial tendon at risk for injury. The present study demonstrated that, in addition to the risk of direct damage to the tendon at the time of screw placement, screws positioned posterior to the anterior colliculus can directly abut the posterior tibial tendon (all ten specimens had contact in Zone 3 and four had contact in Zone 2), a relationship that may lead to pain and degeneration of the posterior tibial tendon because of chronic irritation.

While this study was designed to closely represent a situation that may be seen in routine clinical practice in the treatment of medial malleolar fractures, it was necessary to make a number of methodological assumptions that may have had an effect on the final results. The use of the triple guide and the selection of the center and most distal aspect of the anterior colliculus for the placement of the first screw ultimately determined the placement of the remaining two screws and may have predisposed the placement of these screws in proximity to the posterior tibial tendon. In this series, the average distance from the anterior aspect of the anterior colliculus to the center of the intercollicular groove was 12 mm (range, 11 to 15 mm). This could allow for the placement of two screws into the anterior colliculus in some larger specimens, on the basis of the minimum allowable distance between the screws of 5 mm, as dictated by the triple guide. However, in smaller specimens, the use of the triple guide can lead to placement of the middle screw too far posteriorly and can increase the chance of tendon damage and abutment. Larger fracture fragments approaching a vertical shear pattern can be amenable to more proximal screw placement, but more proximal screw placement closer to the fracture line in a typical oblique fracture can lead to comminution and loss of fixation. A related clinical point is that, because the intimate relationship of the tendon to the posterior tibial groove (Figs. 2 and 3) necessitates having a smooth gliding surface, sharp fragments of comminuted bone at this location may have the same potential as chronic hardware abutment to cause a deleterious effect on the posterior tibial tendon. We believe that this aspect of medial malleolar fracture reduction should be routinely considered and addressed at the time of operative treatment.

Zone 1 (the anterior colliculus) is the "safe zone" for the placement of a medial malleolar screw. Our preferred technique for the placement of medial malleolar screws in Zone 2 or 3 involves direct visualization and retraction of the posterior tibial tendon in order to avoid damaging it during screw-track preparation and screw placement. Visualization of the posterior tibial tendon can be obtained by incising the superficial deltoid ligament and the retinaculum of the posterior tibial tendon directly inferior to the medial malleolus in line with the posterior tibial tendon. This exposure can then be used to confirm maximal seating of the screw to avoid or minimize abutment. By maintaining the retinacular attachment to the posterior aspect of the medial malleolus, the tendon will be maintained in a stable position. The incision can be closed with absorbable sutures, but care should be taken to not pass the suture through the tendon. Placement of a screw in Zone 2 should be into the apex of the intercollicular groove, which may necessitate foregoing the use of a triple guide or placing the Zone-2 screw first and the Zone-1 screw second. If the fracture pattern allows countersinking, this may be considered. If the medial malleolar fracture pattern requires hardware placement into the posterior colliculus, we consider planned hardware removal after fracture-healing in order to avoid the ill effects of chronic abutment of the posterior tibial tendon. ?

References

Materials and Methods | Results | Discussion | References

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Topics

fracture ; ankle ; bone screws ; bone wires ; computers ; tissue dissection ; limb ; fluoroscopy ; fracture fixation ; inferior colliculus

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John E. Femino, Brian F. Gruber, Madhav A. Karunakar; Safe Zone for the Placement of Medial Malleolar Screws. The Journal of Bone & Joint Surgery. 2007 Jan;89(1):133-138.

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