Summary

RADIOLOGICAL SPINE POSITIONING ON THE TIBIAL PLATEAU AND THE IMPLICATIONS FOR HTO PLANNING

Abstract

Objective

The lateral tibial eminence has often been suggested as an appropriate target while aiming the weight bearing line (WBL) in valgus-producing high tibial osteotomy (HTO) procedures. The primary objective was to characterize the position of the medial and lateral tibial eminence on 2-D and 3-D imaging in the average HTO patient population. Secondly, the study evaluated the consistency in planned tibiofemoral alignment while aiming the WBL on the lateral eminence in HTO.

Methods

Tibial eminence positions originating from 70 HTO cases were retrospectively studied on preoperative full-leg standing radiographs and computed tomography (CT) scans. Eminence position was expressed as percentage of the width of the tibial plateau (medial border 0%, lateral border 100%). Osteophytes that could potentially enlarge the size of the tibial plateau were consciously excluded (PACS). 3-D models of the tibia were derived from the CT-scan in Mimics 23.0 and measurements were conducted in 3-matic 14.0 (Materialise, Leuven).
Another 100 preoperative HTO full-leg standing radiographs were reviewed to evaluate consistency in tibiofemoral alignment during HTO planning. The tibial eminence positions (%), the mechanical femorotibial angle (mFTA°) and the mechanical medial proximal tibial angle (mMPTA°) were determined (mean±SD [range], PACS). After conducting the preoperative planning for each case with the WBL crossing the tip of the lateral eminence, the ‘planned’ mFTA and mMPTA were measured (Dugdale method). All measurements were conducted in two-fold by two blinded observers. The intraclass correlation coefficient (ICC) and the eminence imaging correlation statistics were performed in SPSS 26.0.

Results

For the 70 HTO cases, the medial tibial eminence was located at 41.8%±1.9 [38-47%] in 2-D and 42.2%±2.0 [38-48%] in 3-D showing a high correlation (r=0.8271 (0.7349 to 0.8893)). The lateral tibial eminence was located at 58.3%±1.9 [55-63%] in 2-D and 57.3%±2.2 [53-63%] in 3-D showing a high correlation (r=0.7657 (0.6472 to 0.8481)). A good to excellent ICC (ranging 0.8346-0.9193) was observed. For the 100 HTO cases only measured in 2-D, the medial eminence was positioned at 42.1%±1.7 [38-47%], the lateral eminence at 58.5%±1.8 [54-65%], the preoperative mFTA was 173.8°±2.3 [167.8-177.5°], and mMPTA 85.8°±2.2 [81.5-91.2°]. While aiming the WBL on the lateral eminence, the planned mFTA was 181,8°±0.3 [181.2-182.5°] and the mMPTA was 93.8°±2.2 [89.2-100.7°]. The ICC was found to be good for the planned mFTA (0.804) and excellent for all other parameters (ranging 0.953–0.995).

Conclusion

Although frequently used as a target while planning corrections for HTO procedures, little is known about the exact position and variance of the lateral tibial eminence throughout the population. This study found that, in the average HTO patient, the medial and lateral eminences are located at respectively 42% and 57-58% on the tibia plateau with both showing a 10% maximal variance. Good agreement between the 2-D and 3-D imaging modalities was found while evaluating tibial eminence positions in the coronal plane. Furthermore, aiming the WBL through the lateral tibial eminence during HTO planning, will consistently produce 2° of valgus (±1°) mFTA. Meanwhile, the planned mMPTA remains highly dependent on the existing bony varus deformity of the tibia.