Instrumentation and mini-invasive approach in mobile bearing prostheses [Strumentazione e accesso mini-invasivo nelle protesi a piatto mobile]

Description

Aim. Mobile polyethilenic beating was introduced in the design of knee prostheses in the early 80s with the aim to join motion, surface congruity and low contact stress. Based on the successful results achieved after over 20 years experience, mobile bearing knee prostheses are now widely used all over the world. Genesis® Mobile Bearing Knee is characterized by a flat and polished tibial plateau (CoCr alloy) with an anterior plug working as a stop for a poly bearing able to multidirectional motion. Additionally, the bearing motion can be restricted by using a screw stopping translation: in this condition the bearing becomes able of rotation only. The aim of this paper was to assess short-term results of a group of mobile knee prostheses obtained with conventional technique and mini-invasive technique. Methods. At the Orthopaedic Department of Genoa University from October 2003 to June 2004 we implanted 51 Genesis® Mobile Bearing knee prostheses in 51 patients (mean age 67.8 years), because of arthritis in all the cases. In 30 patients we performed a less invasive surgical approach (midvastus) with respect of the quadriceps tendon and without patella dislocation (9 cases: conventional incision and set of instruments: 21 cases: short medial incision - 7/10 cm - and dedicated set of instruments). Results. The midvastus approach have improved patellar tracking: only 3/30 patients (1%) need lateral release. All the 51 patients have been evaluated with a follow up ranging from 19 months to 11 months, with the aim to evaluate the clinical impact of both mobile bearing and less invasive surgical approach. Clinical results (Knee Society Score System) can be resumed as follows: excellent in 26 cases (51%), good in 16 cases (31%), fair in 6 cases (12%) and bad in 3 cases (6%). All the patients, especially those in which a less invasive approach had been used, have shown a faster recovery and a wider range of motion, reasonably related to the above mentioned improved patellar tracking. One patient has shown a limited range of motion and 3 patients have complained about spread mild pain and swelling: however, these results are scantily significant because of the too short follow up. Two patients, in which the bearing motion was restricted by the screw, have complained about postero-lateral pain during flexion, due to impingement with the popliteus tendon: this could be a real problem, caused by either the shape of the bearing (too high posterior edge) and the restricted translation. Conclusion. Even if in our experience there is a very short follow-up, the results obtained have been encouraging at least at very short term as to a rapid recovery and a wider range of motion; however, it should be underlined that these results become overlapping at middle-term.

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