Group A: Patients suffering from midfoot arthritis after failed prior conservative therapy who undergo a reverse distal metatarsal minimal-invasive osteotomy Group B: Patients suffering from midfoot arthritis after failed prior conservative therapy who undergo a fusion of one or more midfoot (tarsometatarsal) joints

Midfoot arthritis is a common condition leading to disabling chronic foot pain that affects activities of daily living. The causes can be primary osteoarthritis (OA), inflammatory or post-traumatic. We are looking at OA of the lesser (second and/or third) tarsometatarasal joints (TMTJ). Orthotics, customised shoes or steroid injections are options to treat this condition nonoperatively. If these measures fail, arthrodesis of the arthritic joints represents the standard procedure to surgical treatment. Generally, the results of this procedure are at a satisfactory level for the patients, nevertheless, there is a relevant amount of patients with residual pain, lack of a normal foot appearance, and the need for unplanned surgery or use of orthotics postoperatively. Furthermore, patients undergoing an arthrodesis of the lesser TMTJ usually have to stay in hospital for 4-7 days. Postoperatively, patients are only allowed to partially weightbear for at least 6 weeks and need a cast for six weeks as well. During that time thrombosis prophylaxis is administered for about 6 weeks.

The conventional distal minimal-invasive metatarsal osteotomy (DMMO) is an accepted technique for metatarsal osteotomies. Recently, Schneider et al. presented results of a modification of the conventional DMMO, the reverse DMMO to treat OA of the lesser TMTJ, thus representing an alternative treatment to arthrodesis. The procedure has many benefits. It allows outpatient care, an immobilisation in a cast is not necessary. Instead, patients have to wear a flat postoperative shoe for 2-3 weeks and are allowed to fully weightbear from day one after surgery. Therefore, thrombosis prophylaxis is not necessary unless there are specific risk factors.

However, while the arthrodesis directly addresses the arthritic joints, the R-DMMO alters the ground reaction force of the metatarsal head leading to less stress at the level of the TMTJ, but the arthritic joint itself is not approached. Still, the results presented by Schneider et al. are promising. Since there was no group to compare the treatment with, the small sample size, and a retrospective design, we would like to prospectively compare these two surgical procedures directly in order to find out whether or not the R-DMMO can be recommended as a standard procedure for OA of the lesser TMTJ at a much more convenient level for patients regarding the whole perioperative protocol. No vulnerable population is included. The scientific value is remarkable since this would be the first study to examine this matter and we are able to provide a high level of evidence due to the prospective-randomised and comparative design of the study. All legal requirements will be fulfilled and the ethical standards are guaranteed.

Both procedures have been described and the technique of the DMMO itself is not new, but its modification (R-DMMO) represents a new approach for this condition. Both procedures are reliable and safe, which is why the risk category of the study is A according to ClinO, Art. 61.

Inclusion Criteria:

• Patients older than 18 years
• Midfoot arthritis of lesser TMTJ (second, third, rarely fourth and fifth) with ongoing disabling pain
• Able to give informed consent as documented by signature
• failed conservative treatment for a period of at least 3 months (CSI injections and/or orthotic devices)

Exclusion Criteria:

• Concomitant fusion of 1st TMTJ
• Patients younger than 18 years
• Contraindication to undergo surgery or general anaesthesia
• Inability to follow the procedures of the study, e.g. due to language problems, psychological disorders, dementia, etc.
• pregnancy