The impact of a high tibial valgus osteotomy and unicondylar medial arthroplasty on the treatment for knee osteoarthritis: a meta-analysis - Spahn, G; Hofmann, G O; von Engelhardt, L V; Li, M; Neubauer, H; Klinger, H M (Knee Surg Sports Traumatol Arthrosc, 2013)