Objectives

Few reports were shown about the position of the cup in total hip arthroplasty (THA) with CT-based navigation system. We use minimally invasive surgery (MIS) technique when we perform cementless THA and the correct settings of cups are sometimes difficult in MIS. So we use CT-based navigation system for put implants with correct angles and positions. We evaluated the depth of cup which was shown on intra-operative navigation system.

Objectives

Many reports were shown about the angle of the cup in total hip arthroplasty (THA) with CT-based navigation system. However, there are few reports about the position of the stem. We investigated the position of the stem in navigated THA. We evaluated the position and alignment of stem which were shown on intra-operative navigation system.

We have devised a combined pillar score (CPS) system, based on the lateral pillar (LP) and the posterior pillar (PP) classifications, together with the age at onset of Perthes’ disease, and examined its correlation with prognosis. The correlation coefficient of the Catterall classification, LP, PP, and CPS systems with the Stulberg system was 0.39, 0.52, 0.50, and 0.70, respectively. Overall 21 of the 22 hips (95.4%) with a CPS of 0 to 1 point had a good outcome and 12 of the 13 hips (92.3%) with a CPS of 3 points or more had a fair or poor outcome. None with a CPS of 2 points, had a poor outcome. The study shows that an accurate prediction of the prognosis is not possible with the LP classification alone for patients classified as belonging to group B (LP height 50% to 100% of contralateral height). The CPS system does allow accurate prediction of outcome.

The authors added a classification of posterior pillars to Herring’s classification of lateral pillars in a retrospective study of 33 patients with Perthes disease. Anteroposterior and frog position lateral radiographs taken approximately two months later from first visit, were evaluated. All patients were treated by a non-weight-bearing method (continuous traction and wheel chair activity). The outcome was evaluated by the Stulberg method.

The mean age at follow-up was 18 years (range,14.2 to 26.9 years).

Thirteen hips were in Catterall group II, 18 were in group III, and two were in group IV. Twenty-five of the 33 hips were in Stulberg class I or II (with good results), and eight hips were class III. Nine hips were in Herring group A, 20 hips were in group B, and four were in group C. Eleven hips were in our group A with the posterior pillar classification, 16 were in group B, and six were in group C. Group A, with a lateral or posterior pillar had good results without exception. Concerning Herring’s classification, all four heads had become aspherical in group C, however, 16 hips were good results and four hips were poor in group B. The outcome was poorly related to the classification in 20 patients with 20 affected hips in Herring group B when only lateral pillars were used in classification. When both lateral and posterior pillars are considered in classification, results can be predicted more accurately than when only lateral pillars are considered. This more accurate prognosis at an early stage of Perthes disease can facilitate effective treatment selection.