Computertomography/Robot-assisted Retrograde Drilling of Osteochondral Lesions of the Ankle Joint Martin Wiewiorski, MD, Andre Leumann, MD, Geert Pagenstert, MD, Arno Frigg, MD, and Victor Valderrabano, MD, PhD Abstract: The aim of this article is to describe a novel computer- tomography-guided robot-assisted surgery technique for retrograde drilling of osteochondral lesions of the talus and distal tibia. Key Words: osteochondral lesions, talus, ankle joint, cartilage (Tech Foot & Ankle 2011;10: 139–143) HISTORICAL PERSPECTIVE Several arthroscopically guided techniques have been de- scribed for treatment of osteochondral lesions (OCL) of the talus and the distal tibia, such as debridement, anterograde drilling, microfracturing, or curettage. 1–4 However, all trans- articular approaches involve possible disruption of potentially still viable articular cartilage and supplementary damage to bone and soft tissues. 5 To leave the cartilaginous surface intact and allow improved addressing of the bony component of the lesion, a transtalar retrograde drilling technique has been introduced by Conti and Taranow. 6 A drill guide is inserted through an arthroscopical portal and positioned in the lesion to allow percutaneous drilling through the sinus tarsi. The position of the guidewire and drill bit is controlled under fluoroscopy. The lesion is curetted through the drill cavity and filled with cancelous bone. Good results in terms of functional outcome and postoperative pain have been demonstrated. 5 However, this challenging procedure demands excellent coordination of the arthroscopic view with the estimated drill trajectory. Talus anatomy and tight intra-articular space of the ankle joint make lesion localization and instrument access difficult, especially at the posterior talar edge. The use of drill guides is technically insufficient if the lesion cannot be exactly localized by arthroscopic view and fluoroscopy, as seen in early stages of the disease. Repetitive drilling attempts with failure rates as high as 20% have been reported. 5,7 The excellent ability of computertomography (CT) for skeletal imaging allows easy and exact identification of OCL. Bale et al 8 described good accuracy in CT-assisted, navigated retrograde drilling of talar OCL. Their technique is a multistage procedure with an initial fabrication of a removable custom-made fixation cast. CT imaging and navigation are performed preinterventionally. The actual surgery is performed subsequently without CT guidance. This system relies on the rigid retention of the preoperatively assessed cast position in relation to the ankle. In case of a malpositioned guidewire it requires conversion to fluoroscopically guided intraoperative adjustment. To overcome those issues, a technique using a robotic assistance device (INNOMOTION, Herxheim, Germany) was developed. 9 It previously showed its value for magnetic resonance imaging (MRI) and CT-guided clinical interven- tional procedures, such as foot joint, facet joint, sacroiliac joint infiltrations, and other musculoskeletal interventions. 9–13 INDICATIONS AND CONTRAINDICATIONS Inclusion Criteria  Osteochondral lesions of the talus or distal tibia.  Intact cartilage cover on MRI (type V according to Hepple et al 14 ).  Focal, cystic osseus lesion with intact roof on CT or single photon emission computed tomography-com- puted tomography (SPECT-CT) (type I according to Ferkel 15 ).  Lesion <1.5 cm 2 .  Patients aged from 18 to 55 years.  Primary procedure. Exclusion Criteria  Failure of previous surgical treatment.  Metabolic arthropathies.  Kissing lesions.  Major, nonreconstructable defects.  Chronic inflammatory systemic disorders.  Obesity (body mass index >30). Preoperative Planning Clinical examination of the ankle joint includes documentation of range of motion, sagittal and inversion/eversion stability, location of pressure pain, and alignment of the hindfoot. Initial diagnostic imaging of the foot and ankle consist of plain radiographs (weight-bearing standard anteroposterior/ lateral radiographs, Saltzman view) to assess alignment and exclude degenerative joint disease other than an OCL. MRI is performed to examine the morphology of the cartilage above the cystic lesion. To adequately assess the extent of the bony lesion and the amount of remodeling activity, we additionally perform a 99m Tc-dicarboxypropandiphosphate SPECT-CT. Inte- grated hybrid systems like the SPECT-CT are a new approach allowing acquisition of functional SPECT images and anatomical CT images in a single diagnostic procedure. 16 We use SPECT-CT as part of a routine algorithm for diagnostics of all degenerative joint disease of the foot and ankle joints. 17 TECHNIQUE Technical Setting Surgery was performed with a CE-certified robotic assistance device (INNOMOTION, Innomedic) mounted on the table of a multislice CT scanner (SOMATOM Sensation 10, Siemens, From the Orthopaedic Department, University Hospital Basel, Basel, Switzerland. The authors declare no conflict of interest. Address correspondence and reprint requests to Victor Valderrabano, MD, PhD, Orthopaedic Department, University Hospital of Basel, Spitalstrasse 21, 4031 Basel, Switzerland. E-mail: vvalderrabano@uhbs.ch. Copyright r 2011 by Lippincott Williams & Wilkins SPECIAL FOCUS Techniques in Foot & Ankle Surgery  Volume 10, Number 4, December 2011 www.techfootankle.com | 139