SLR - July 2014 - Christopher Schroeder

Computed Tomography of the Ankle in Full Plantar Flexion: A Reliable Method for Preoperative Planning of Arthroscopic Access to Osteochondral Defects of the Talus
Reference: van Bergen CJ, Tuijthof GJ, Blankevoort L, Mario M, Kerkhoffs GM and van Dijk CN.
Computed Tomography of the Ankle in Full Plantar Flexion: A Reliable Method for Preoperative Planning of Arthroscopic Access to Osteochondral Defects of the Talus. The Journal of Arthroscopic and Related Surgery, 2012-07-01, Volume 28, Issue 7, Pages 985-992.

Scientific Literature Review

Reviewed By: Christopher M. Schroeder, DPM
Residency Program: Forest Hills Hospital North Shore LIJ Forest Hills, New York

Podiatric Relevance: Osteochondral defects of the talus involve the articular cartilage and subchondral bone, and are usually located in the central or posterior third of the medial or lateral talar dome. Primary surgical treatment is arthroscopic debridement and microfracture. Access to the defect is restricted by the tibal plafond. To gain exposure to the OCD the foot must be put into maximum plantar flexion. Some defects located in the posterior aspect can become challenging to gain access due to location of the defect or limited range of motion. Accurate preoperative planning will assist the surgeon in choosing whether anterior arthroscopy or another surgical approach would be appropriate. CT scanning is the preferred preoperative planning. CT scanning is normally performed with the ankle joint in a platargrade position, but is different from the plantar-flexed ankle on anterior ankle arthroscopy. CT in a full plantar-flexed positioning simulating the arthroscopic position represents the boney morphology with the arthroscopic measurements for preoperative planning. The article hypothesized the location of the OCD in relation to the anterior distal tibial rim on CT scan of a fully plantar-flexed ankle would correlate with the location as measured during anterior ankle arthroscopy.  

Methods: Prospective study with patients that were 18 years of age with suspected and diagnosed OCD of the talus were included. CT scans of the affected ankle in both plantigrade and fully plantar-flexed positions were obtained with the use of a metal-free 3-demensional footplate. The accessibility of the OCD was defined by the distance between the anterior border of the OCD and the anterior distal tibial rim. The distance was measured on sagittal CT reconstructions and compared with anterior ankle arthroscopy as the reference standard. Measurements were taken from the anterior border of the OCD (most anterior point of the boney lesion) and the anterior distal tibial rim. All patients where placed in a supine position and anteromedial and anterolateral portals were created at the level of the joint line. A 4-mm, 30 degree arthroscope was used and the anterior border of the defect was identified and marked with an arthroscope hook. The surgeon then measured the anteroposterior distance between the anterior border of the OCD and the anterior distal tibial rim with the patient’s ankle in full plantar flexion. In more difficult cases a portion or entire defect as removed to gain more exposure and then measured. The intraobserver and interobserver reliability of the CT measurements was analyzed by computation of intraclass correlation coefficients and systematic differences with 95 percent confidence intervals. The correlation of CT and arthroscopic measurements was analyzed by the Pearson correlation coefficient. A scatter plot and linear regression analysis were used to analyze the relation between CT and arthroscopy.

Results: Twenty consecutive patients, 17 men and three women, with a mean age of 33 years, which included 10 left and 10 right ankles were analyzed. Mean degree of plantar flexion was 42 degrees. OCD lesion locations: 10 centromedial talar dome, four posteromedial, three centrolateral, one posterolateral, one anteriolateral and one centrocentral. Both intraobserver and interobserver reliability was excellent (ICC, 0.998 and 0.997, respectively; P < .001). The intraobserver systematic difference was not statistically significant (mean, 0.051 mm, 95 percent CI, -0.061 to 0.15mm), but there was a significant interobserver systemic difference (mean, 0.37 mm; 95 percent CI, 0.24 to 0.50 mm, P < .001). There was an excellent correlation (r = 0.975, P < .001) between CT and arthroscopy. There was no statistically significant systematic difference (mean, 0.36 mm; 95 percent CI, -0.051 to 0.77).

Conclusions:  Measurements on CT scans of the ankle in full plantar flexion are a reliable and accurate preoperative method to determine the in situ arthroscopic location of talar OCDs. There was only one patient with a difference between CT and arthroscopy greater then 2.0 mm. The intraobserver and the interobserver reliability of measurement on CT was excellent. There was no statistically significant intraobserver systematic difference. However, the interobserver systematic difference was 0.37 mm. This difference is so small that it may not be clinically relevant.

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