VOL. 84-B, NO. 3, APRIL 2002 457 F. S. Wang, PhD K. D. Yang, MD, PhD R. F. Chen, MS Department of Medical Research C. J. Wang, MD, Director Department of Orthopaedic Surgery S. M. Sheen-Chen, MD Department of General Surgery Chang Gung Memorial Hospital, Kaohsiung, Taiwan. Correspondence should be sent to Dr C. J Wang at 123 Ta-Pei Road, Niao- Sung, Kaohsiung 833, Taiwan. ©2002 British Editorial Society of Bone and Joint Surgery 0301-620X/02/311609 $2.00 Extracorporeal shock wave promotes growth and differentiation of bone-marrow stromal cells towards osteoprogenitors associated with induction of TGF-1 F. S. Wang, K. D. Yang, R. F. Chen, C. J. Wang, S. M. Sheen-Chen From Chang Gung Memorial Hospital and Chang Gung University, Kaohsiung, Taiwan E xtracorporeal shock-wave (ESW) treatment has been shown to be effective in promoting the healing of fractures. We aimed to determine whether ESW could enhance the growth of bone-marrow osteoprogenitor cells. We applied ESW to the left femur of rats 10 mm above the knee at 0.16 mJ/mm 2 in a range of between 250 and 2000 impulses. Bone-marrow cells were harvested after ESW for one day and subjected to assessment of colony-forming unit (CFU) granulocytes, monocytes, erythocytes, megakaryocytes (CFU-Mix), CFU-stromal cells (CFU-S) and CFU-osteoprogenitors (CFU-O). We found that the mean value for the CFU-O colonies after treatment with 500 impulses of ESW was 168.2 CFU-O/well (SEM 11.3) compared with 88.2 CFU-O/well (SEM 7.2) in the control group. By contrast, ESW treatment did not affect haematopoiesis as shown by the CFU-Mix (p = 0.557). Treatment with 250 and 500 impulses promoted CFU-O, but not CFU-Mix formations whereas treatment with more than 750 impulses had an inhibiting effect. Treatment with 500 impulses also enhanced the activity of bone alkaline phosphatase in the subculture of CFU-O (p<0.01), indicating a selective promotion of growth of osteoprogenitor cells. Similarly, formation of bone nodules in the long-term culture of bone-marrow osteoprogenitor cells was also significantly enhanced by ESW treatment with 500 impulses. The mean production of TGF-1 was 610 pg/ml (SEM 84.6) in culture supernatants from ESW-treated rats compared with 283 pg/ml (SEM 36.8) in the control group. Our findings suggest that optimal treatment with ESW could enhance rat bone-marrow stromal growth and differentiation towards osteoprogenitors presumably by induction of TGF-1. J Bone Joint Surg [Br] 2002;84-B:457-61. Received 8 August 2000; Accepted after revision 9 March 2001 Extracorporeal shock-wave (ESW) therapy has been shown to have a promising effect on the treatment of tendino- pathies and the healing of fractures. 1-5 Experimental studies on cell lines or vessels have indicated that ESW can cause damage. 6,7 Haupt et al 8 first identified that ESW could enhance osteogenic activity, but the mechanism by which it promotes bone healing in fractures remains to be deter- mined. We hypothesised that it may promote the growth and differentiation of bone-marrow mesenchymal cells pre- sumably by the induction of osteogenic growth factors such as transforming growth factor beta 1 (TGF-1). It is known that bone-marrow mesenchymal stromal cells have the potential to differentiate into osteoprogenitors and several musculoskeletal-related cell lineages. 9,10 These osteoprogenitors produce bone matrices resulting in a scaf- fold for bone growth. 11,12 The production of TGF-1 in the bone-marrow microenvironment has an important role in regulating and stimulating the differentiation of osteopro- genitors during the repair of fractures in vivo 13,14 and in vitro. 15-18 Our aim was to investigate whether ESW could promote bone-marrow osteoprogenitor cell growth in asso- ciation with the induction of TGF-1. Materials and Methods We used 50 four-month-old male Sprague-Dawley rats (National Experimental Animals Production Centre, Taipei, Taiwan). Eight were used in the pilot study and the other 42 were randomly divided into seven groups of six. They were anaesthetised by an intraperitoneal injection of pentobarbi- tal sodium (50 mg/kg; Nembutal sodium, Abbott Labo- ratories, Illinois) and placed supine with all four limbs in abducent extensional fixation. ESW treatment at 0.16 mJ/ mm 2 (Ossatron HMT High Medical Technologies GmbH, Kreuzlingen, Switzerland) was applied to the left distal femur 10 mm above the knee. Ultrasound transmission gel (Pharmaceutical Innovations Inc, New Jersey) was used as