Minimal invasive surgery is a modern concept of keeping the skin incision and the soft tissue trauma at surgery as small as possible. In hip arthroplasty the important gluteal muscles are preserved by an anterior or antero-lateral surgical approach, minimizing possible muscle injury. The patients experience less pain after surgery and early mobilisation. Special implants have been designed to faciilitate implantation of the prosthesis by smaller skin incisions and less bone loss. (e.g. AMIS or ALMIS method) Hip prostheses, which are implanted without bone cement are usually made of TITANIUM. This is the method of choice in most countries in central Europe. Titanium shows an excellent bone ingrowth and there are nearly no allergies or adverse reactions against this material. Once the prosthesis is ingrown, loosening is very rare. The gliding surface in hips is ceramic or crosslinked polyethylen. Knee endoprostheses are mainly implanted with bone cement and are made of different metal alloys. Due to excellent longterm results in central Europe (Austria, Swizerland, Germany) cementless implantation of Titanium hip prostheses is the method of choice. In this type of fixation, the bone grows directly into the surface of the prostheses and formes a durable connection. More recently, hydroxy appatit surface of the prostheses accelerates bony ingrowth.
Knee endoprostheses are widely implanted with bone cement. This is a 2 component substance, which hardens within 15 minutes and forms immediatly a stable interface between bone and prosthesis. Return to sports after joint arthroplasties is possible after 3 to 12 months after surgery. "low impact" sports (e.g. swimming, biking, walking, hiking, scating, golf etc.) are recommended. Tennis, dancing, cross country skiing and optional downhill skiing can be performed according to the preoperative level. "High impact" sports like soccer, jumping, baseball, basket ball are not recommended.
More detailed recommendations can be given on the basis of the surgical result, the implant used and the status of previous sport activities. Most of the reasons, causing loosening of endoprostheses are solved today. New gliding surfaces (ceramics, crosslinked polyethylen, vitamin E inforced polyethylen) produce less particle wear and proved much longer durability than 20 years at in vitro tests. Aseptic loosening of high quality implants is very rare. Once a cementless implant is fixed, only fracture and infection may cause early loosening.
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