Abdominal Wall

The superficial layers of the abdominal wall include the skin, subcutaneous fascia, and fatty layers separating them. The muscular wall of the abdomen is composed of differing layers depending on the medial or lateral location of examination. The abdominal wall is composed of three muscle layers lateral to the abdominal rectus muscle—the external and internal oblique muscles and the transversus abdominis muscle. Each layer has associated fascial extensions that come together to make up the anterior and posterior rectus sheath surrounding the rectus muscle medially. Deep to these layers is the transversalis fascia and the peritoneum with a variable amount of preperitoneal fat interspersed between these two layers. As this layer progresses laterally, the peritoneum thickens and becomes less densely adherent to its adjacent tissue layer.

The posterior musculature includes the psoas major muscle immediately lateral to the lumbar spine. Lateral to the psoas muscle is the quadratus lumborum muscle superiorly and the iliacus muscle inferiorly transitioning at approximately the L4 level. At the more superior disc levels (approximately L2-3 and cephalad), the tendinous and muscular slips of the diaphragm start to form anteriorly on the spine itself. The right crus of the diaphragm inserts into L3, and the left crus inserts into L2. They are tendinous at this point and need to be taken down to expose L2-3. For L3-4, the right crus needs to be taken down for exposure all the way to the right side. These do not need to be repaired.

Retroperitoneal Structures

The primary nonvascular system of concern for the access surgeon is the genitourinary tract. On the left side, the ureter courses with its blood supply and the gonadal vessels until the ureter tracks medially over the iliac vessels at approximately the level of the common iliac artery bifurcation. More superiorly, the left kidney and its surrounding perirenal fat and fascia are encountered. Care must be taken when mobilizing the ureter to avoid devascularizing it with excessive dissection; this can be accomplished by maintaining the ureteral packet with the peritoneum, to which it is adherent.

Vascular Anatomy: Variability, Bifurcations, Iliolumbar Vein, Segmental Vessels, and Middle Sacral Vessels

The distal aorta and the distal vena cava with their respective bifurcations provide the primary structures of consequence to the immediate anterior surface of the lumbosacral region. The aorta sits to the left of the vena cava, in approximation with the midline of the spine, with its major branches typically crossing anterior to the venous branches of the cava. The vena cava sits to the right side of the spine, which is why right-sided approaches are more hazardous.

The vascular anatomy is reviewed in a caudad-to-cephalad order because this is the order of most common to least common levels of approach. The vasculature at the L5-S1 level generally consists of the middle sacral vessels, which can be divided between ligatures or cauterized, depending on their size. The vena cava bifurcation is generally superior to the L5-S1 disc and overlies the L5 vertebral body on the right side, although in a small percentage of individuals this is seated as low as the inferior edge of the L5-S1 disc itself. It bifurcates to the left and right common iliac veins.

Rarely, anomalous venous drainage may be present across the sacral spine. This may include a single vessel as a bridging iliac vein to a confluent venous plexus across the region. The iliolumbar vein typically branches off posterior to the common iliac vein at the L5 vertebral level and is an important consideration for exposure for the L4-5 disc space above. Most of the time, it may be identified within 2 cm of the L4-5 disc space. In a small percentage of patients, it may not be present. The common iliac artery can be easily visualized lateral to the vein and is usually bifurcating into the internal and external iliac arteries at the L5-S1 level.

The vascular anatomy at the L4-5 level is the most variable of all the levels and can provide either a boon or a bane to the access surgeon depending on its layout. Much has been described in scoring systems for the degree of difficulty this variability presents; however, it does not alter the general approach strategy. The aortic bifurcation and the cava bifurcation make up the variable vascular distribution for L4-5. This consideration is only for the amount of relative length that would be obtained when mobilizing the left common iliac artery, not for dissecting out the aortic bifurcation itself.

Generally, the caval bifurcation is at the L5 vertebral body. The aortic bifurcation sits between L4 and L5, although it is usually located superior to the L4-5 disc space. The left common iliac artery courses laterally from this and has a variable degree of length and tortuosity to it. Cephalad to the L4-5 level are the segmental vessels that cross over the vertebral bodies to enter the aorta. The dissection is to elevate the left common iliac artery to decrease the amount of tension on the vessel. In some instances of a high-riding aortic bifurcation, the common iliac artery is able to be maintained in a lateral position. Otherwise, complete mobilization is generally needed to maintain this vessel in a right-sided location relative to the face of the L4-5 disc during a left-sided approach.

Lymphatics

The lymphatics run in parallel to the vasculature surrounding the lumbar spine. The fatty tissue encompassing them may be increased in obese individuals or may be increased secondary to inflammatory processes. Disruption of the lymphatics occurs when exposing the L4-5 level and higher, although clinically significant lymphoceles or mild lymphedema is rare. Generally, the lymphatics track to the lateral aspect of the spine region between the vasculature and the psoas muscle.

Nerves

There are several nerves of importance that run in proximity to the field of dissection for a lumbosacral spine approach. In descending order, the somatic nerves lateral to the psoas muscle include the iliohypogastric nerve, ilioinguinal nerve, and lateral femoral cutaneous nerve. The genitofemoral nerve runs along the anterior surface of the psoas muscle before branching into the laterally located femoral branch and the medially located genital branch.

The sympathetic chain runs in parallel to the spine, along the lateralmost aspect of the anterior face of the vertebral body. Small bridging fibers can be seen coursing medially. The superior hypogastric plexus takes its form around the L5 level. These fibers are variable in their substance and can be viewed in forms ranging from a discrete nerve to a diffuse plexus as it courses inferiorly. They form upward to become the left and right hypogastric nerves, which are an important supply of sympathetic function in the pelvis. Injury to this nerve can cause retrograde ejaculation in men. These fibers are relatively adherent to the peritoneum and generally are mobilized as one structure, along with the ureter.

Preoperative Considerations

Communication is the mainstay to a successful partnership between the spine surgeon and access surgeon and the supporting surgical team. Before the day of surgery, relevant radiologic imaging will have been obtained and reviewed to determine the surgical plan. Any additional imaging should be pursued at that time to take into account disease processes that the patient may have. Examining plain films for signs of arterial calcifications, which may provide indirect evidence of vascular disease (Fig. 19–1), is particularly useful for the access surgeon. Additionally, the plain film should be evaluated for osteophytes and spondylolisthesis, which can exaggerate misleading anatomic bony features or be an indicator of potential inflammatory changes. A thorough vascular examination should be repeated at the time of surgery. Pulse oximetry on the patient’s left lower extremity is a useful adjunct for monitoring arterial flow distal to the area of dissection. Positioning of the patient is important to facilitate intraoperative placement of personnel, fixed retraction, and fluoroscopy machines.

FIGURE 19–1 Calcification of aorta and common iliac artery (arrow).

General Considerations

There are two general anatomic routes for anterior exposure to the lumbar spine—transperitoneal and retroperitoneal. Several techniques have been described for both anatomic routes. Generally, these can be distinguished as open techniques and laparoscopic or robotic assisted techniques. These techniques may vary from institution to institution based on access and preference of the spine surgeon, anatomic considerations, and type of spine operation being considered (type of fusion vs. disc replacement vs. oncologic intervention). There are advantages and disadvantages to both techniques, although there is generally a lower complication profile with an anterior retroperitoneal approach versus a transperitoneal approach.

With a higher associated complication rate, the open transperitoneal approach should be used only when extenuating circumstances exist (e.g., revision surgery or prior extensive retroperitoneal surgery) and not for primary open exposures. There are otherwise no advantages to performing a primary case transperitoneally from L2 to S1 because all these levels can be reached via a retroperitoneal route almost all the time. For access surgeons who use robotic or laparoscopic techniques in their transperitoneal approach, this may offset some of the risk.

Open Approaches

Retroperitoneal

The retroperitoneal approach can proceed from various incisions, including vertical midline, paramedian, oblique, and transverse. Extensive lateral incisions should be avoided because this may denervate medially situated rectus muscle. The incision needs to take into account the spinal level and the number of lumbar levels to be exposed. An infraumbilical transverse incision can accommodate most approaches to the L4-5 and L5-S1 disc levels, whereas a more obliquely oriented incision is favored for access to disc levels above L4 (Figs. 19-2 and 19-3). This incision allows for access to the L2-3 disc level and possibly L1-2 disc level in patients with a favorable body habitus.

FIGURE 19–2 Approximate level of incision for approach of disc levels.

FIGURE 19–3 Skin marking for L5-S1 approach.

The operative procedure should begin after an appropriate review of the films and after surgical goals have been established between the access surgeon and the spine surgeon. Communication with all members of the team is important to establish the surgical plan of the case and to decrease the risk of complications. Review of relevant radiographic material by the access surgeon can show potential deviations from normal anatomy and is the first step toward risk reduction. At that time, the relative position of the L4-5 disc level to the superior iliac crest can be identified.

Lateral fluoroscopy can be used to assess the level of the incision (Fig. 19–4). This imaging is done in conjunction with a radiopaque probe or rod to determine the angle of the approach and level, which can be marked on the patient’s abdomen. Fluoroscopy can be especially important in obese patients because there may be no other anatomic landmarks palpable to guide the placement of the abdominal incision (Fig. 19–5). In most nonobese patients, palpation by an experienced access surgeon can be used to locate the sacral prominence to identify the L5-S1 disc space. A transverse approach to the L4-5 level should be directed at approximately the level of the superior anterior iliac spine, although fluoroscopic confirmation should be used if there is any question. All of the landmarks can be confirmed by fluoroscopic guidance, and fluoroscopy is especially important in patients who have distorted spine anatomy, had prior spine surgery, or are obese.

FIGURE 19–4 Radiologic determination of angle of approach for L5-S1 disc level.

FIGURE 19–5 A, Lateral view of lumbar spine. B, Lateral view of patient.

When the level has been determined, the incision is made and cautery is used to deepen this to the level of the anterior rectus sheath fascia. The fascia is transversely or obliquely incised, and superior and inferior fascial flaps are raised at the linea alba. Care should be taken in patients who have had previous Pfannenstiel incisions because they may have unrecognized midline incisional hernias. The mobilization of the fascial flaps provides for less tethering of the deeper tissues and rectus muscle. The left rectus muscle is bluntly mobilized to a lateral position, taking care to identify the inferior epigastric vessels and small perforators. By dissecting deep to these vessels, they can be preserved; however, they can be clipped and divided if necessary.

Inspection and gentle finger dissection can be used to identify the inferior edge of the posterior rectus sheath. This provides the landmark to begin blunt separation of the peritoneal cavity laterally to start the exposure into the retroperitoneal space (Fig. 19–6). Standing on the patient’s right side allows the access surgeon to take advantage of the natural motion of his or her hand to roll the peritoneum in a medial direction, although many surgeons proceed with the approach from the left side to maintain direct visualization of the vasculature (Fig. 19–7). The left ureter easily rolls up as part of this maneuver. The landmark to feel for is the bulge of the psoas muscle and the pulse of the common iliac artery. A common mistake is to persist in aggressive dissection lateral to the psoas muscle thinking that the planes may be adhesed. In almost all virgin retroperitoneal spaces, the blunt dissection should be able to be accomplished easily and without use of force (Fig. 19–8).

FIGURE 19–6 A, Initial approach to the retroperitoneum. B, Initial approach with the peritoneum separating away from the posterior rectus fascia.

FIGURE 19–7 A, Initial line of approach once past the deep lateral margin of the posterior rectus sheath. B, View of the retroperitoneal structures with the peritoneal packet partially medialized.

FIGURE 19–8 Approach to retroperitoneum with the peritoneal packet mobilized medially.

When the peritoneum has started to roll medially, and the iliac artery has been palpated, the next landmark to be palpated should be the L5-S1 disc level. Feeling for this prominence (comparing anatomic structures with the expected findings of the preoperative radiographs) lets the access surgeon confirm that the appropriate plane has been mobilized. In patients who have significantly abnormal anterior spine anatomy, plain films should be used to confirm location. Fixed or table-mounted retraction can be set to hold back the peritoneum and abdominal wall structures with secondary retractors (either table-mounted or hand-held) used for vascular structures. The ureter should be identified in its retroperitoneal course, and care should be taken to protect it. The arterial structures should be gently palpated at this point to evaluate their baseline and to feel for any evidence of plaque disease or thrills. When the initial peritoneal mobilization has been performed, the access surgeon may shift to the patient’s left side; this provides for a more direct view of the lateral aspects of the vascular structures.

The L5-S1 disc space can be mobilized with the use of Kittner dissectors. The middle sacral vessels can be mobilized and divided between ligatures or small clips. The surgeon should be judicious in the use of clips because they may become dislodged or caught during dissection of the spine. Blunt dissection generally can be used to expose the entire face of the L5-S1 disc level without significant need for major vascular mobilization (Fig. 19–9). Care should be taken during the mobilization to elevate the superior hypogastric plexus with the peritoneum. This plexus typically feels like a fibrous band within the peritoneal fat and typically elevates with the peritoneal packet.

FIGURE 19–9 Exposure of L5-S1 disc.

The L4-5 disc level is generally the most difficult level to provide full access to for the spine surgeon. The degree of difficulty can be established preoperatively with computed tomography (CT) angiography or magnetic resonance angiography, although angiography is generally unnecessary for most routine cases using open techniques. It is also important to look for vascular calcifications because calcification increases the potential risk for complications with an exposure at the L4-5 level. The transverse incision can be lengthened or obliqued based on the body mass and build of the patient.

The exposure can proceed as described earlier. After the retroperitoneum has been exposed, vascular mobilization is needed to access the L4-5 disc. A plain film can be obtained to confirm the disc level. Gentle blunt dissection can be used to mobilize the left common iliac artery. This dissection should be continued distally well onto the external iliac artery to minimize potential trauma to the artery. Generally, the vascular structures should be mobilized as paired structures, to minimize the “hazard” areas. Separating the vein and artery provides a 360-degree perimeter of vascular structures and is not recommended under routine circumstances. If it is a high bifurcation, a thorough mobilization of the left common iliac artery and vein may allow them to be retracted laterally. Gentle Kittner dissection shows the iliolumbar vein as it branches off the posterolateral aspect of the common iliac vein, inferior to the L4-5 disc. If it is not identified within approximately 15 to 20 mm of the disc space, it may not impede the exposure and may be left intact. Aggressive attempts at identifying the iliolumbar vein beyond this range may increase the risk of injury to the nerve roots in the region.

It is important to divide the vessel securely when there appears to be tethering because excessive traction on this structure can cause tearing with associated significant blood loss. Additional mobilization of the segmental vessels immediately adjacent and superior to the L4-5 region is sometimes necessary (Fig. 19–10). Pulse oximetry is important when mobilizing the L4-5 disc space or higher. Before retraction or mobilization, the oxygen saturation and waveform of a left lower extremity pulse oximeter should be evaluated. When retraction has been applied, if the saturation diminishes to zero, the surgeon has approximately 45 to 50 minutes before the retraction should be released to allow for resumption of unimpeded blood flow. The waveform should normalize over a brief period before replacement of the retractors. This can be repeated with periodic release of the retractors every 30 minutes or so after that. If there is not a return to baseline over a few minutes, vascular examination with ultrasound should be performed to minimize the risk of a missed injury or thrombosis.

FIGURE 19–10 Exposure of L4-5 disc.

Approaches to the lumbar spine above L4 can be through a transverse or more obliquely oriented incision. The abdominal wall is divided in layers to expose the peritoneum directly. Care must be taken in using blunt dissection to gain access to the retroperitoneal space. When completed, fixed retraction can be especially useful to maintain the level of exposure without lengthening the incision. Kittner dissection is used to mobilize the disc level, which can be confirmed with plain film evaluation.

Laparoscopic or Robotic Approach

Laparoscopic or robotic minimally invasive approaches have been used over the last 10 years as more attention has been given to overall patient recovery and length of stay. The immediacy of improvement with minimally invasive spine approaches has not followed the same pathway as for other general surgical procedures. The improvements in length of stay and cosmesis are sometimes seen but usually at a tradeoff of prolonged operative times and increased complication rates. These approaches are technically more complicated and are not in uniform or widespread use and have generally been superseded by the mini-open approach.^1–3

As with open approaches, there are two general routes by which access surgeons perform laparoscopic approaches—transperitoneal and retroperitoneal. There are additional permutations to these types of approaches based on the type of spine intervention being performed and on whether the approach is fully laparoscopic or laparoscopic-assisted.

The transperitoneal approach involves the same maneuvers on the inside as described for the open approach. Fluoroscopy is used to site appropriately the level of the approach device being used. Two to four trocars are inserted to provide retraction for the bowel while mobilizing the peritoneum over the L5-S1 disc space. After the exposure has been completed laparoscopically, one of two steps can be taken. If the anterior fusion is being performed through guide tubes, a small incision can be made just large enough to accommodate the guide. It is positioned with lap guidance, and then the spine surgeon performs the fusion. Alternatively, the surgeon may place a small assist device, such as a hand port or wound protector device, to splint open a small incision to allow the spine surgeon to work directly.

Adapting minimally invasive surgery to the retroperitoneal approach has been slightly more challenging. Multiple techniques have been developed, but are based on laparoscopic or laparoscopic-assisted principles. With fluoroscopic guidance, the level of the disc is marked on the patient’s abdomen. Using a lateral or oblique approach, an open trocar technique is used to access the retroperitoneal space. A balloon dissector or finger dissection can be used for the initial development of the space. Under direct vision, the balloon is insufflated to develop the retroperitoneal space mechanically. The balloon is then exchanged for a regular 10-mm trocar, and an additional two to three ports are placed as needed; this is usually done in a stepwise fashion as the space is developed further. Soft-tipped retractors and Kittners are used to mobilize the field at the indicated levels, using fluoroscopy as needed for guidance.

After the exposure has been completed in this fashion, the spine surgeon can be set up in a similar fashion as for the laparoscopic transperitoneal approach. This approach may be especially useful in obese patients who need a single-level exposure above L5. This approach would allow for the direct mobilization of the tissue surrounding the level that would otherwise be unable to be obtained without making a larger incision. There may also be an increasing role for this approach for spine surgeons who perform lateral lumbar interbody fusion.

Additional Exposure Considerations

There has been an evolution of the treatment algorithm of back pain with the continued development of motion-preserving disc replacement products. As greater numbers of patients undergo disc replacement, there is likely to be an accompanying need for revision surgery. Although the need for anterior revisions for acute problems has been uncommon, this is likely to increase with time as the parts typically sustain wear and tear as observed for other joint prostheses. For patients who are undergoing surgery at the L5-S1 level, the surgeon may use a right-sided approach to preserve the tissues planes in case it becomes necessary to return to the retroperitoneum.

For all levels, vascular protection “patches” are being used for twofold effect. The first is as a barrier interface to prevent vascular ingrowth and scarring into the discectomy space. Preservation of separate layers helps revision surgeons reaccess the space with less potential morbidity to the vasculature. Second, the inert barrier may provide a guide path through the surrounding scar tissue planes to reach the area of the disc. Although review of strategies for revision access is beyond the scope of this chapter, consideration for possible future revision at the time of the primary procedure would help to reduce the considerable morbidity associated with these procedures.

Complications

Complications secondary to anterior lumbar exposure can be minimized with a thorough knowledge of the anatomy and of the spine surgeon’s operative technique. There is the potential for complications during the access phase of the operation and during the instrumentation phase, both of which need to be anticipated to minimize the risk.

During the initial exposure, appropriate precautions must be taken in any patient who has had prior lower abdominal surgery or disease states, ranging from procedures such as inguinal hernia repairs to cesarean sections to pathologic gynecologic disease or diverticulitis. Pediatric urologic procedures can be especially dangerous because the details may not be known by the patient. Male patients with prior hernia repairs with mesh may experience same-side testicular pain postoperatively, and this should be discussed ahead of time. Each can contribute to making the tissue planes more difficult to navigate. The access surgeon must always be suspicious for the potential of ventral or incisional hernias in any patient with lower abdominal scars.

Sharp dissection can be used to minimize cautery trauma while dissecting tissue planes around potential hernia sites. As dissection proceeds into the retroperitoneal planes, care must be taken not to apply undue force to mobilize them. Filmy avascular planes should be able to be manipulated with only a small amount of effort. Additional effort or need for cautery may be suggestive of veering into the wrong plane. Care should be taken to include the gonadal vessels and the left ureter en bloc with the medialized peritoneum because this provides the safest first step toward protecting the ureter. If there is doubt about any tubular structure, the surgeon should delay dividing it until it has been completely examined and identified.

Tears in the peritoneum usually can be primarily repaired at this time to help maintain the integrity of the cavity. This repair facilitates retraction and helps minimize potential injury to intra-abdominal organs, especially the intestines. If injury does occur with exposure of luminal contents to the working field, consideration should be given to deferring further surgical intervention until the bowel injury has had time to heal (minimum of 3 to 5 days, ideally 2 to 3 months). Excessive use of cautery in proximity to the bowel or by metal retractors should also be avoided because of the risk of indirect burn injury. This injury can manifest as a delayed bowel injury several days to weeks later. Also at higher levels of exposure, consideration must be given to protecting the spleen, to minimize potential retractor trauma to this fragile organ.

When the primary retractors are set to hold the peritoneum, the vascular dissection can begin (either under direct vision or with laparoscopic visualization). In noninflamed tissue, gentle vascular mobilization can be accomplished with the use of peanut dissectors and a vein retractor. Clearly identified venous branches should be divided between ligatures to minimize avulsion injuries. The left iliolumbar vein can be easily avulsed during the exposure of the L4-5 disc space if this is not controlled during vascular mobilization (Fig. 19–11). The variable location of this vein may account for part of the significantly higher rate of vascular injury at this level.⁴ This vascular injury can lead to significant bleeding, which may be difficult to control if the distal end retracts. Small (<1 mm) venous branches can be cauterized to decrease the risk of larger venous avulsion injury. Most small venous tears can be controlled with mild direct pressure with or without topical thrombotic agents. Venous injuries that are on an exposed surface or in the angle of retraction should be controlled with a small monofilament suture on a taper needle if necessary. This suture decreases the risk of propagation into a large venous injury; however, it may increase the risk of postoperative thrombosis at the site of repair.

FIGURE 19–11 Anterior view of L4-5 disc.

Arterial injuries can occur at the time of dissection but are more likely to occur during instrumentation or secondary to retractor compression. Small segmental arteries should be controlled while mobilizing levels greater than L5, and the middle sacral artery can be divided between ligatures along with the vein. Direct major arterial injury is rare but can be catastrophic if it occurs.

The arterial and venous structures are at risk during the period of instrumentation. Vessels that are under tension are more susceptible to extensive sharp injury than when in situ. Both structures can be traumatized by instrumentation against fixed field retraction to cause a scissoring or pinching effect. The ureter is also at risk for this type of injury. Arterial bruising can propagate a small vascular wall hematoma into a thrombotic event secondary to direct or indirect trauma. Thrombosis of the left common iliac artery is the most common arterial complication.^5–7 “Snap” injuries can also occur where the artery is quickly moved from one position to another. In patients who have palpable atherosclerotic plaque disease, there may be an increased risk of thromboembolic events. It is important to perform a full vascular mobilization of the left common and external iliac arteries to decrease the potential risk of injury secondary to stretch or angulation. This injury can give rise to the formation of a plaque lip, which could give rise to a mural thrombosis, which could then propagate. It is important to check frequently the pulse examination of the distal extent of the exposed left external and internal iliac arteries and to use continuous pulse oximetry to minimize potential rare arterial injuries.

Few nerve structures are directly at risk during lumbosacral exposure. The hypogastric nerve is a potential source of injury, however, with significant clinical consequences, especially in men. The expected rate of retrograde ejaculation should be less than 1%, but the reported rate is 0 to 5.9%.⁸ The incidence of retrograde ejaculation is increased 10-fold with a transperitoneal approach versus a retroperitoneal approach.⁹ Expectant management shows resolution of the problem in 50% to 80% of patients over 6 to 12 months; however, it is best avoided by a retroperitoneal approach and careful dissection. Sympathetic injury can lead to a hyperthermic response in the corresponding left lower extremity with subsequent feeling of increased warmth and mild edema. This condition also resolves over 6 to 12 months, but permanent autoregulatory dysfunction can occur in rare cases. Additional nerve injuries are rare and are usually related to compression injuries of the lateral abdominal wall somatic nerves causing temporary dermal hypoesthesias.

Lymphatic injury is rarely clinically significant, although there are case reports of lymphoceles developing after approach procedures. Generally, if there is a need for aggressive lymphatic dissection, small clips can be applied, especially if lymph is noted to be draining into the surgical field. If a lymphocele develops, percutaneous drainage can be performed with radiologic guidance. Drains should not be left in anticipation of leakage because this may increase the risk of infection.

Infectious complications, although rare, can be devastating and educational. Superficial wound infections can be treated with local drainage and antibiotic therapy and rarely lead to deep infection. Deep space infection is rare and occurs in less than 1% of patients.¹⁰ Presentation of deep infection would lead to concern over a possible missed injury with subsequent field contamination, although this can be supported further by culture results. Late presentation may occur years after the initial operation.