Patient-specific instrumentation (PSI) has been greatly marketed in knee endoprosthetics for the past few years. By utilising PSI, the prosthesis´ accuracy of fit should be improved. Besides, both surgical time and hospital costs should be reduced. Whether these proposed advantages are achieved in medial UKA remains unclear yet. The aim of this study was to evaluate the preoperative planning accuracy, time saving, and cost effectiveness utilising PSI in UKA.

Data from 22 patients (24 knees) with isolated medial unicompartmental knee osteoarthritis were analysed retrospectively. The sample comprised sixteen men and six women (mean age 61 ± 8 years) who were electively provided with a UKA utilising PSI between June 2012 and October 2014. For evaluation of preoperative planning accuracy (1) planned vs. implanted femoral component size, (2) planned vs. implanted tibial component size, and (3) planned vs. implanted polyethylene insert size were analysed. Since UKA is a less common, technically demanding surgery, depending in large part on the surgeon´s experience, preoperative planning reliability was also evaluated with regard to surgeon experience. Moreover, actual surgical time and cost effectiveness utilising PSI was evaluated.

Preoperative planning had to be modified intraoperatively to a wide extend for gaining an optimal outcome. The femoral component had to be adjusted in 41.7% of all cases, the tibial component in 58.3%, and the insert in 87.5%. Less experienced surgeons had to change preoperative planning more often than experienced surgeons. Utilising PSI increased surgical time regardless of experience. Linear regression revealed PSI-planning and surgeon inexperience as main predictors for increased surgical time. Additionally, PSI increased surgical costs due to e.g. enlarged surgical time, license fees and extraordinary expenditure for MRI scans.

The preoperative planning accuracy depends on many different factors. The advertised advantages of PSI could not be fully supported in case of UKA on the basis of the here presented data – especially not for the inexperienced surgeon.

Introduction: Previous investigation showed that joint distraction (arthrodiastasis) is able to reduce intraarticular pressure and to have a positive effect on the regeneration of bone and cartilage on both sides of the joint. Many reports have been published about the results of arthrodiastasis in the treatment of femoral head necrosis in young children, pointing out good reconfiguration of the femoral head and improved range of motion. In contrast to that, -to our knowledge- there is so far no study showing the effect of hip joint distraction in older children with femoral head avascular necrosis.

Question: In the present study the outcome of the treatment of femoral head avascular necrosis in older children by hip joint distraction was investigated.

Methods: The hip joint distraction method was performed in three patients with necrosis of the femoral head. The causes of avascular necrosis were: Late onset Perthes’ disease in two patients and slipped capital femoral epiphysis (ECF) in one patient. The average age of the patients was 13.4 years. They all suffered from persistent severe pain and mostly limited range of motion of the hip joint. The plain radiographs revealed a Catterall IV, Herring C stade in both patients with late onset Perthes’disease. In the radiograph of the ECF patient a severe deformity of the femoral head was visible. After intraoperative soft tissue release, joint distraction was performed with an Ilizarov-ring fixation and immediately distracted 4–5 mm under image control. Distraction was continued 1 mm per day until the Shenton line was overcorrected. At this time the fixator was changed so that flexion-extension exercises were encouraged with the fixator in place. The patients were kept non-weight bearing. After 4 weeks the fixator was changed, so that in addition abduction up to 30° was possible. In total fixator duration time was 3.5 months. (In one case due to a fracture, the fixator was left for further 3 months) During distraction period with the fixator two patients suffered a femoral fracture without a causal adequate trauma.

Due to these major complications further investigations on additional patients have been stopped.

Results: The outcomes after 2.5 years showed in two patients an ankylosis of the hip joint with adductionflexion contracture and radiographical no reshaping of the femoral head. The third patient had a poor range of motion while radiographic findings showed a good reconfiguration of the femoral head. Nevertheless even in this patient advanced arthrosis was evident.

Conclusion: In conclusion, due to the major complications and the unsatisfactory “middle-term”-results, arthrodiastasis as a therapy of avascular necrosis of the femoral head in older children has failed in our study. In our opinion fracture was as a result of immobilisation osteopenie.