Some stretching of the ipsilateral psoas and lumbar plexus is unavoidable when “breaking” the bed at the level of the hip to enlarge the costo­pelvic angle. While not necessary in every patient, this maneuver is generally required for access to the L4–L5 level and when operating within the concavity of a scoliotic deformity and should be performed judiciously. Placement of a roll under the contralateral hip may in some cases decrease or eliminate the need to “break” the operating table and may result in less stretching of the ipsilateral psoas and lumbar plexus.

Assiduous use of active neuromonitoring (EMG) minimizes the risk of direct injury to the spinal nerves and motor branches of the lumbar plexus but does not herald impending injury to the sensory branches, including the genitofemo­ral, ilioinguinal, and iliohypogastric nerves (Fig. 27.1 ). Injury to the genitofemoral nerve, which emerges from the ventral aspect of the psoas muscle around the L3–L4 level and is therefore most frequently at risk during the trans­psoas approach, is thought to be responsible for postoperative painful dysesthesias of the ipsilat­eral groin and anteromedial thigh. It is diffi cult to distinguish this injury from thigh pain resulting from a general lumbar plexus traction neura­praxia and/or direct psoas trauma; regardless postoperative thigh pain of some form has been reported in most series as an early, typically tran­sient, complication [ 15 , 18 , 19 ]. Indeed, in their review of the largest series published to date, Rodgers et al. report that transient thigh pain and hip fl exor weakness – which they attribute to direct psoas trauma – is a nearly universal fi nding [ 16 ]. Cummock et al., in a recent publication, have provided some initial data on the duration of these symptoms, which in their experience resolve by 3 months in 50 % of patients and by 1 year in greater than 90 % of patients [ 3 ]. In our experience, some patients also complain of dys­esthetic pain extending ventrally from the fl ank incision(s), which may be due to injury to cutane­ous nerves and responds in most cases to neuro­modulatory medications such as gabapentin and pregabalin.

Avoidance of approach-related complications begins prior to incision, ensuring that the patient is positioned so that a true lateral image and an anteroposterior image are projected with the fl uo­roscope at right angles to the fl oor. This decreases the likelihood of bringing the abdominal viscera further into the operative corridor. When planning the incision(s), it may be advantageous to consider the local pattern of Langer’s lines as the risk of transection of cutaneous nerves – and of the post­operative fl ank and anterior abdominal wall dyses­thetic pain syndromes thought to result therefrom – may be less when the incision(s) are made paral­lel to these lines. Next, confi rmation of proper entry into the retroperitoneum is critical, facilitated by careful preoperative review of magnetic resonance or computed tomography imaging. The authors uti­lize the posterolateral incision in most lateral approach cases (and in all cases involving rota- tional deformity) and emphasize the importance of blunt fi nger dissection at a 45° angle to the plane of the spine, so as not to lose one’s orientation and risk entrapment of peritoneum. Passage through the transversalis fascia and into the retroperitoneum is typically achievable without the need for sharp dis­section, avoidance of which may limit the risk of injury to the retroperitoneal viscera. Thorough, gentle mobilization of the peritoneal viscera anteri­orly, away from the operative corridor, is critical.

attendant risks of graft malposition, subsidence, and migration. Also worthy of mention, however, is the potential for many of the injuries – previ­ously discussed in the context of the exposure and retractor placement – to occur on the contra- lateral side as a result of maneuvers during the discectomy and graft insertion steps of the proce­dure. It is essential, using fl uoroscopic imaging if necessary, to remain aware at all times of the depth of insertion of the instruments used during the discectomy. This is particularly true when using the Cobb elevator to open the contralateral portion of the annulus fi brosus and break any bridging anterolateral osteophytes (Fig. 27.4 ), which risks injury to the contralateral nerve root and psoas muscle and may lead to the develop­ment of a contralateral retroperitoneal hematoma [ 13 ]. All of the visceral structures discussed in the preceding section – including the ureter, kidney, pleura, lung parenchyma, and great ves­sels – might theoretically be injured on the side opposite the approach, particularly in the setting of rotational deformity.